Tissue products derived from animals lacking any expression of functional alpha 1, 3 galactosyltransferase

ABSTRACT

The present invention provides tissues derived from animals, which lack any expression of functional alpha 1,3 galactosyltransferase (alpha-1,3-GT). Such tissues can be used in the field of xenotransplantation, such as orthopedic reconstruction and repair, skin repair and internal tissue repair or as medical devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/334,194, filed on Dec. 22, 2011, which is a continuation of U.S.patent application Ser. No. 11/083,393, filed Mar. 17, 2005, now U.S.Pat. No. 8,106,251, which claims priority to U.S. Provisional PatentApplication No. 60/553,895, filed on Mar. 17, 2004 and U.S. ProvisionalPatent Application No. 60/559,816, filed on Apr. 6, 2004. U.S. patentapplication No. 13/334,194 is a continuation-in-part of U.S. patentapplication Ser. No. 10/646,970, filed on Aug. 21, 2003, now U.S. Pat.No. 7,795,493, which claims priority to U.S. Provisional PatentApplication No. 60/404,775, filed on Aug. 21, 2002.

FIELD OF THE INVENTION

The present invention provides tissues derived from animals which lackany expression of functional alpha 1,3 galactosyltransferase(alpha1,3GT). Such tissues can be used in the field ofxenotransplantations, such as orthopedic reconstruction and repair, skinrepair and internal tissue repair, or as medical devices.

BACKGROUND OF THE INVENTION

Ruminant animals, such as porcine, ovine and bovine, are consideredlikely sources of xenograft organs and tissues. Porcine xenografts havebeen given the most attention since the supply of pigs is plentiful,breeding programs are well established, and their size and physiologyare compatible with humans. Other ruminant sources, such as bovine orovine have also been suggested as a source for hard and soft tissuexenografts. However, there are several obstacles that must be overcomebefore the transfer of these organs or tissues into humans can besuccessful. The most significant is immune rejection. The firstimmunological hurdle is “hyperacute rejection” (HAR). HAR is defined bythe ubiquitous presence of high titers of pre-formed natural antibodiesbinding to the foreign tissue. The binding of these natural antibodiesto target epitopes on the donor tissue endothelium is believed to be theinitiating event in HAR. This binding, within minutes of perfusion ofthe donor tissue with the recipient blood, is followed by complementactivation, platelet and fibrin deposition, and ultimately byinterstitial edema and hemorrhage in the donor organ, all of which causerejection of the tissue in the recipient (Strahan et al. (1996)Frontiers in Bioscience 1, e34-41).

The most frequently transplanted tissue in humans is bone (J. M. Lane etal. Current Approaches to Experimental Bone Grafting, 18 OrthopedicClinics of North America (2) 213 (1987)). In the United States alonemore than 100,000 bone graft or implant procedures are performed everyyear to repair or replace osseous defects resulting from trauma,infection, congenital malformation, or malignancy. Human bone is a hardconnective tissue consisting of cells embedded in an extracellularmatrix of mineralized ground substance and collagen fibers (Stedman'sMedical Dictionary, Williams & Wilkins, Baltimore, Md. (1995)).

Bone grafts and implants are often formed of autologous bone. However,transplantable autologous bone tissue for large defects, particularly inchildren, is often unavailable. In addition, autologous bonetransplantation may result in postoperative morbidity such as pain,hemorrhage, wound problems, cosmetic disability, infection or nervedamage at the donor site. Further, difficulties in fabricating thedesired functional shape from the transplanted autologous bone tissuecan result in less than optimal filling of the bone defect.

Soft tissues, such as tendons, ligaments, cartilage, skin, heart tissueand valves, and submucosal tissues, are also commonly transplanted intohumans. Much of the structure and many of the properties of the originaltissue can be retained in transplants through use of xenograftmaterials. Xenograft tissue represents an unlimited supply of availablematerial if it can be processed to be safe for transplantation in ahuman.

Once implanted in an individual, a xenograft provokes immunogenicreactions such as chronic and hyperacute rejection of the xenograft.Because of this rejection, bone xenografts exhibit increased rates offracture, resorption and nonunion. The major immunological obstacle forthe use of animal tissues, such as porcine, bovine or ovine, as implantsin humans is the natural anti-galactose alpha 1,3-galactose antibody,which comprises approximately 1% of antibodies in humans and monkeys.

Except for Old World monkeys, apes and humans, most mammals carryglycoproteins on their cell surfaces that contain the galactose alpha1,3-galactose epitope (Galili et al., J. Biol. Chem. 263: 17755-17762,1988). In contrast, glycoproteins that contain galactose alpha1,3-galactose are found in large amounts on cells of other mammals, suchas pigs. Humans, apes and old world monkeys do not have a galactosealpha 1,3-galactose and have a naturally occurring anti-galactose alpha1,3-galactose antibody that is produced in high quantity (Cooper et al.,Lancet 342:682-683, 1993). It binds specifically to glycoproteins andglycolipids bearing galactose alpha-1,3 galactose.

This differential distribution of the “alpha-1,3 GT epitope” andanti-Gal antibodies (i.e., antibodies binding to glycoproteins andglycolipids bearing galactose alpha-1,3 galactose) in mammals is theresult of an evolutionary process which selected for species withinactivated (i.e. mutated) alpha-1,3-galactosyltransferase in ancestralOld World primates and humans. Thus, humans are “natural knockouts” ofalpha-1,3-GT. A direct outcome of this event is the rejection ofxenografts, such as the rejection of pig organs transplanted into humansinitially via HAR.

A variety of strategies have been implemented to eliminate or modulatethe anti-Gal humoral response caused by porcine xenotransplantation,including enzymatic removal of the epitope with alpha-galactosidases(Stone et al., Transplantation 63: 640-645, 1997), specific anti-galantibody removal (Ye et al., Transplantation 58: 330-337, 1994), cappingof the epitope with other carbohydrate moieties, which failed toeliminate alpha-1,3-GT expression (Tanemura et al., J. Biol. Chem.27321: 16421-16425, 1998 and Koike et al., Xenotransplantation 4:147-153, 1997) and the introduction of complement inhibitory proteins(Dalmasso et al., Clin. Exp. Immunol. 86: 31-35, 1991, Dalmasso et al.Transplantation 52:530-533 (1991)). Costa et al. (FASEB J 13, 1762(1999)) reported that competitive inhibition of alpha-1,3-GT inH-transferase transgenic pigs results in only partial reduction inepitope numbers. Similarly, Miyagawa et al. (J Biol. Chem 276, 39310(2001)) reported that attempts to block expression of gal epitopes inN-acetylglucosaminyltransferase III transgenic pigs also resulted inonly partial reduction of gal epitopes numbers and failed tosignificantly extend graft survival in primate recipients.

Badylak et. al. developed a process to isolate submucosa tissue from thesmall intestine of pigs for use in a variety of tissue grafts includingconnective tissue grafts to repair knee ligaments (anterior cruciateligament) and shoulder rotator cuff repair. The small intestinesubmucosa (SIS) material is treated using chemical and enzymatic stepsto strip the tissue of viable cells, leaving an acellular extracellularmatrix that encourages in-growth of host cells and tissue regeneration(see, for example, U.S. Pat. Nos. 4,902,508, 4,956,178, and 5,372,821).This process is currently utilized for human tissue grafts. However,despite the chemical treatment steps, galactose alpha 1,3 galactosesugar residues remain embedded in the graft and cause immune activationand inflammation in human patients (Allman et al., 2001, Transplantation71, 1631-1640; Mcpherson et al., 2000, Tissue Engineering 6(3),233-239).

Stone et al. developed a process to treat porcine soft tissue and bonetissue to remove cellular material followed by treatment withalpha-galactosylsidase to remove the galactose alpha 1,3-galactose fromthe tissue prior to transplantation (Stone et al. Transplantation 1997:63: 646-651; Stone et al. Transplantation 1998: 65:1577-83). Thisprocess has been the subject of numerous patent applications, whichdiscuss the use of such tissue for a variety of applications, such asanterior cruciate ligament repair, meniscal repair, articular cartilagexenografts, submucosal xenografts, bone and bone matrix xenografts,heart valve replacement and soft tissue xenografts, see for example,U.S. Pat. Nos. 5,865,849, 5,913,900, 5,984,858, 6,093,204, 6,267,786,6,455,309, 6,683,732, 5,944,755, 6,110,206, 6,402,783, and 5,902,338;U.S. Patent Application Nos. 2002/0087211, 2001/0051828, 2001/0039459,2003/0039678, 2003/0023304, and 2003/0097179; and PCT Publication Nos.WO 00/47131, WO 00/47132, WO 99/44533, WO 02/076337, WO 99/51170, WO99/47080, WO 03/097809, WO 02/089711, WO 01/91671, and WO 03/105737.

Thus, there is a need in the art to provide tissue grafts that do notcause deleterious effects in humans.

Costa et al. (FASEB (2003) 17: 109-111) reported that the delayedrejection of porcine cartilage transplanted into wild-type andα-1,3-galactosyltransferase knockout mice is reduced by transgenicexpression of α1,2-fucosyltransferase (HT transgenic) in the cartilage.

Single allele knockouts of the alpha-1,3-GT locus in porcine cells andlive animals have been reported. Denning et al. (Nature Biotechnology19: 559-562, 2001) reported the targeted gene deletion of one allele ofthe alpha-1,3-GT gene in sheep. Harrison et al. (Transgenics Research11: 143-150, 2002) reported the production of heterozygous alpha-1,3-GTknock out somatic porcine fetal fibroblasts cells. In 2002, Lai et al.(Science 295: 1089-1092, 2002) and Dai et al. (Nature Biotechnology 20:251-255, 2002) reported the production of pigs, in which one allele ofthe alpha-1,3-GT gene was successfully rendered inactive. Ramsoondar etal. (Biol of Reproduc 69, 437-445 (2003)) reported the generation ofheterozygous alpha-1,3-GT knockout pigs that also express humanalpha-1,2-fucosyltransferase (HT), which expressed both the HT andalpha-1,3-GT epitopes.

PCT publication No. WO 94/21799 and U.S. Pat. No. 5,821,117 to theAustin Research Institute; PCT publication No. WO 95/20661 to Bresatec;and PCT publication No. WO 95/28412, U.S. Pat. No. 6,153,428, U.S. Pat.No. 6,413,769 and US publication No. 2003/0014770 to BioTransplant, Inc.and The General Hospital Corporation provide a discussion of theproduction of alpha-1,3-GT negative porcine cells based on knowledge ofthe cDNA of the alpha-1,3-GT gene (and without knowledge of the genomicorganization or sequence). However, there was no evidence that suchcells were actually produced prior to the filing date of theseapplications and the examples were all prophetic.

The first public disclosure of the successful production of aheterozygous alpha-1,3-GT negative porcine cell occurred in July 1999 atthe Lake Tahoe Transgenic Animal Conference (David Ayares, PPLTherapeutics, Inc., “Gene Targeting in Livestock”, Transgenic AnimalResearch Cinference, July 1999, Abstract, pg. 20; Ayares, IBS NewsReport, November 1999: 5-6). Until recently, no one had published orpublicly disclosed the production of a homozygous alpha 1,3GT negativeporcine cell. Further, since porcine embryonic stem cells have not beenavailable to date, there was and still is no way to use an alpha-1,3-GThomogygous embryonic stem cell to attempt to prepare a live homogygousalpha1,3GT knock out pig.

On Feb. 27, 2003, Sharma et al. (Transplantation 75:430-436 (2003)published a report demonstrating a successful production of fetal pigfibroblast cells homozygous for the knockout of the alpha-1,3-GT gene.

PCT publication No. WO 00/51424 to PPL Therapeutics describes thegenetic modification of somatic cells for nuclear transfer. This patentapplication discloses the genetic disruption of the alpha-1,3-GT gene inporcine somatic cells, and the subsequent use of the nucleus of thesecells lacking at least one copy of the alpha-1,3-GT gene for nucleartransfer.

U.S. Pat. No. 6,331,658 to Cooper & Koren claims but does not confirmany actual production of genetically engineered mammals that express asialyltransferase or a fucosyltransferase protein. The patent assertsthat the genetically engineered mammals would exhibit a reduction ofgalactosylated protein epitopes on the cell surface of the mammal.

PCT publication No. WO 03/055302 to The Curators of the University ofMissouri confirms the production of heterozygous alpha 1,3GT knockoutminiature swine for use in xenotransplantation. This application isgenerally directed to a knockout swine that includes a disruptedalpha-1,3-GT gene, wherein expression of functional alpha-1,3-GT in theknockout swine is decreased as compared to the wildtype. Thisapplication does not provide any guidance as to what extent thealpha-1,3-GT must be decreased such that the swine is useful forxenotransplantation. Further, this application does not provide anyproof that the heterozygous pigs that were produced exhibited adecreased expression of functional alpha1,3GT. Further, while theapplication refers to homozygous alpha 1,3GT knockout swine, there is noevidence in the application that any were actually produced orproducible, much less whether the resultant offspring would be viable orphenotypically useful for xenotransplantation.

Total depletion of the glycoproteins that contain galactose alpha1,3-galactose is clearly the best approach for the production of porcineanimals for xenotransplantation. It is theoretically possible thatdouble knockouts, or the disruption of both copies of the alpha 1,3GTgene, could be produced by two methods: 1) breeding of two single alleleknockout animals to produce progeny, in which case, one would predictbased on Mendelian genetics that one in four should be double knockoutsor 2) genetic modification of the second allele in a cell with apre-existing single knockout. In fact, this has been quite difficult asillustrated by the fact that while the first patent application onknock-out porcine cells was filed in 1993, the first homozygous alpha1,3GT knock out pig was not produced until July 2002 (described herein).

Transgenic mice (not pigs) have historically been the preferred model tostudy the effects of genetic modifications on mammalian physiology, fora number of reasons, not the least of which is that mouse embryonic stemcells have been available while porcine embryonic stem cells have notbeen available. Mice are ideal animals for basic research applicationsbecause they are relatively easy to handle, they reproduce rapidly, andthey can be genetically manipulated at the molecular level. Scientistsuse the mouse models to study the molecular pathologies of a variety ofgenetically based diseases, from colon cancer to mental retardation.Thousands of genetically modified mice have been created to date. A“Mouse Knockout and Mutation Database” has been created by BioMedNet toprovide a comprehensive database of phenotypic and genotypic informationon mouse knockouts and classical mutations(http://research.bmn.com/mkmd; Brandon et al Current Biology5[7]:758-765(1995); Brandon et al Current Biology 5[8]:873-881(1995)),this database provides information on over 3,000 unique genes, whichhave been targeted in the mouse genome to date.

Based on this extensive experience with mice, it has been learned thattransgenic technology has some significant limitations. Because ofdevelopmental defects, many genetically modified mice, especially nullmice created by gene knock out technology die as embryos before theresearcher has a chance to use the model for experimentation. Even ifthe mice survive, they can develop significantly altered phenotypes,which can render them severely disabled, deformed or debilitated (Pray,Leslie, The Scientist 16 [13]: 34 (2002); Smith, The Scientist14[15]:32, (2000); Brandon et al Current Biology 5[6]:625-634(1995);Brandon et al Current Biology 5[7]:758-765(1995); Brandon et al CurrentBiology 5[8]:873-881(1995); http://research.bmn.com/mkmd). Further, ithas been learned that it is not possible to predict whether or not agiven gene plays a critical role in the development of the organism,and, thus, whether elimination of the gene will result in a lethal oraltered phenotype, until the knockout has been successfully created andviable offspring are produced.

Mice have been genetically modified to eliminate functional alpha-1,3-GTexpression. Double-knockout alpha-1,3-GT mice have been produced. Theyare developmentally viable and have normal organs (Thall et al. J BiolChem 270:21437-40(1995); Tearle et al. Transplantation 61:13-19 (1996),see also U.S. Pat. No. 5,849,991). However, two phenotypic abnormalitiesin these mice were apparent. First, all mice develop dense corticalcataracts. Second, the elimination of both alleles of the alpha-1,3-GTgene significantly affected the development of the mice. The mating ofmice heterozygous for the alpha-1,3-GT gene produced genotype ratiosthat deviated significantly from the predicted Mendelian 1:2:1 ratio(Tearle et al. Transplantation 61:13-19 (1996)).

Pigs have a level of cell surface glycoproteins containing galactosealpha 1,3-galactose that is 100-1000 fold higher than found in mice.(Sharma et al. Transplantation 75:430-436 (2003); Galili et al.Transplantation 69:187-190 (2000)). Thus, alpha1,3-GT activity is morecritical and more abundant in the pig than the mouse.

Despite predictions and prophetic statements, no one knew whether thedisruption of both alleles of the alpha-1,3-GT gene would be lethal orwould effect porcine development or result in an altered phenotype(Ayares et al. Graft 4(1) 80-85 (2001); Sharma et al. Transplantation75:430-436 (2003); Porter & Dallman Transplantation 64:1227-1235 (1997);Galili, U. Biochimie 83:557-563 (2001)). Indeed, many experts in thefield expressed serious doubts as to whether homozygous alpha-1,3-GTknockout pigs would be viable at all, much less develop normally. Thus,until a viable double alpha-1,3-GT knockout pig is produced, accordingto those of skill in the art at the time, it was not possible todetermine (i) whether the offspring would be viable or (ii) whether theoffspring would display a phenotype that allows the use of the organsfor transplantation into humans.

Such concerns were expressed until a double knockout pig was produced.In 2003, Phelps et al. (Science 299:411-414 (2003)) reported theproduction of the first live pigs lacking any functional expression ofalpha 1,3 galactosyltransferase, which represented a major breakthroughin xenotransplantation.

PCT publication No. WO 04/028243 filed by Revivicor, Inc. describes thesuccessful production of viable pigs, as well as organs, cells andtissues derived therefrom, lacking any functional expression of alpha1,3 galactosyltransferase. PCT Publication No. WO 04/016742 filed byImmerge Biotherapeutics, Inc. also describes the production of alpha 1,3galactosyltransferase knock-out pigs.

It is therefore an object of the present invention to provide tissueproducts that can be transplanted into humans without causingsignificant rejection.

It is another object of the present invention to provide tissues fromanimals for use in orthopedic reconstruction and repair, skin repair andinternal tissue repair in humans.

SUMMARY OF THE INVENTION

The present invention is tissue products from animals lacking anyexpression of functional alpha-1,3-galactosyltransferase for use asxenografts. The tissue can be hard tissue, such as bone, or soft tissue,such as dermal. This hard and soft tissue can be used as a prosthesis,for example, for use in orthopedic reconstruction and repair, skinrepair and/or internal tissue repair. The animal can be a ruminant or anungulate, such as a bovine, porcine or ovine. In a specific embodiment,the animal is a pig. The tissues from animals lacking any functionalexpression of the alpha-1,3-GT gene can be obtained from a prenatal,neonatal, immature, or fully mature animal, such as a porcine, bovine orovine. The tissues can be prepared according to the methods describedherein for use in animal, such as human, tissue repair.

In embodiments of the present invention, tissues are provided in whichboth alleles of the alpha-1,3-GT gene are rendered inactive, such thatthe resultant alpha-1,3-GT enzyme can no longer generate galactosealpha1,3-galactose on the cell surface. In one embodiment, thealpha-1,3-GT gene can be transcribed into RNA, but not translated intoprotein. In another embodiment, the alpha-1,3-GT gene can be transcribedin an inactive truncated form. Such a truncated RNA may either not betranslated or can be translated into a nonfunctional protein. In analternative embodiment, the alpha-1,3-GT gene can be inactivated in sucha way that no transcription of the gene occurs.

In one aspect of the present invention, tissues are provided in which atleast one allele of the alpha-1,3-GT gene is inactivated via a genetictargeting event. In another aspect of the present invention, tissuesfrom animals are provided in which both alleles of the alpha-1,3-GT geneare inactivated via a genetic targeting event. The gene can be targetedvia homologous recombination. In other embodiments, the gene can bedisrupted, i.e. a portion of the genetic code can be altered, therebyaffecting transcription and/or translation of that segment of the gene.For example, disruption of a gene can occur through substitution,deletion (“knockout”) or insertion (“knockin”) techniques. Additionalgenes for a desired protein or regulatory sequence that modulatetranscription of an existing sequence can also be inserted.

As one aspect of the invention, tissues from animals are provided thatcarry at least one point mutation in the alpha-1,3-GT gene. Such animalsare free of antibiotic-resistance genes and thus have the potential tomake a safer product for human use. Thus, another aspect of theinvention is tissue from a homozygous alpha-1,3-GT knock out that has noantibiotic resistant or other selectable marker genes, such as neomycin,puromycin, hygromycin, zeocin, hisD, or blasticidin. In one embodiment,this point mutation can occur via a genetic targeting event. In anotherembodiment, this point mutation can be naturally occurring. In a furtherembodiment, mutations can be induced in the alpha-1,3-GT gene via amutagenic agent. In one specific embodiment the point mutation can be aT-to-G mutation at the second base of exon 9 of the alpha-1,3-GT gene(see, FIG. 2; Phelps et al. Science 299:411-414 (2003)). In otherembodiments, at least two, at least three, at least four, at least five,at least ten or at least twenty point mutations can exist to render thealpha-1,3-GT gene inactive. In other embodiments, tissues are providedin which both alleles of the alpha-1,3-GT gene contain point mutationsthat prevent any expression of functional alpha-1,3-GT. In a specificembodiment, tissues are provided that contain the T-to-G mutation at thesecond base of exon 9 in both alleles of the alpha-1,3-GT gene. In afurther embodiment, one allele is inactivated by a genetic targetingevent and the other allele is inactivated due to presence of a T-to-Gpoint mutation at the second base of exon 9 of the alpha-1,3-GT gene. Ina specific embodiment, tissues from animals are provided in which oneallele is inactivated via a targeting construct directed to Exon 9 andthe other allele is inactivated due to presence of a T-to-G pointmutation at the second base of exon 9 of the alpha-1,3-GT gene (see,FIG. 2; Phelps et al. Science 299:411-414 (2003)).

In a further embodiment, hard or soft tissue can be obtained fromanimals lacking any functional expression of the alpha-1,3-GT gene thatalso can contain additional genetic modifications. Such geneticmodifications can include additions and/or deletions of other genes toprevent rejection, promote wound healing, and/or minimize or eliminateunwanted pathogens (such as, for example, prions or retroviruses).

In one embodiment, the tissue can be used in its “native” form (directlyremoved from the animal). Alternatively, the tissue can be subjected tofurther treatment or modification. In particular embodiments of thepresent invention, decellularized tissues are provided that are derivedfrom the animals or tissues described herein. Other embodiments providemethods and processes to prepare and obtain the tissue from an animalthat lacks any expression of functional alpha-1,3-galactosyltransferase.

In certain embodiment, processes to prepare tissue can include steps tostrip away or kill all viable cells (decellularization) leaving behindonly an acellular matrix or scaffold for use in tissue repair andremodeling, as well as, optionally, treatments for crosslinking andsterilization. In a particular embodiment, any decellularized hard orsoft tissue is provided that is derived from the animals disclosedherein. In one embodiment, de-cellularized soft dermal tissue isprovided. In another embodiment, de-cellularized submucosal tissue isprovided. In other embodiment, such de-cellularized material can be lessimmunogenic. In further embodiments, such de-cellularized tissues can beused as a scaffolding or matrix to repair and/or reconstruct particularhuman body parts. In one embodiment, the decellularized tissue can beused for the repair of the following, including, but not limited to,hernia, abdominal wall, rotator ciff, cosmetic surgery or any other softtissue defects known to one skilled in the art or disclosed herein. Inparticular embodiments, submucosal and or dermal decellularized materialis provided.

The tissues and the animal source of the tissues can be further modifiedor treated to promote wound healing; minimize or eliminate unwantedpathogens, such as infectious disease transmission (such as prions andretroviruses); add growth factors to promote tissue remodeling,sterilize the tissue, and/or improve the biomechanical or physicalproperties of the tissue. Such treatments can be chemical, such asalcohol or peroxide treatment, mechanical or physical, such as enzymaticand/or exposure to a gas, ultra violet radiation, or gamma irradiation.

In another embodiment, the tissues from animals lacking any functionalexpression of the alpha-1,3-GT gene can be combined with other inertmaterials such as plastics, metals (including but not limited tostainless steel and titanium) in order to provide additional mechanicalstrength or for other benefits to the recipient patient.

In another embodiment, the tissues from animal lacking any functionalexpression of the alpha-1,3-GT gene can be used as a scaffold, whichserves to recruit the recipient's cells to the site of the transplantedmaterial. This scaffold can also contain extracellular matrix (ECM)components, such ECM components can optionally be derived from an animallacking any functional expression of the alpha-1,3-GT gene.Alternatively, the tissue can be used as a complete tissue replacement,such that, for example, the transplanted tissue performs the samebiomechanical functionality of the tissue it is replacing or repairing.In a further embodiment, the tissue can be preconditioned (chemicallyand/or mechanically) prior to transplantation to allow optimal range ofmotion of the tissue following transplantation, or to allow for a“custom fit” for the recipient, or to otherwise provide optimalbiological or biomechanical properties.

In one embodiment of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in orthopedic reconstructionand repair. Such tissues include connective tissue, tendons, ligaments,muscle, cartilage, bone and bone derivatives. In one embodiment, thetissue can be used for knee repair, such as anterior cruciate ligament(ACL) or posterior cruciate ligament (PCL) replacement. In anotherembodiment, the tissue can be used for bone-tendon-bone grafts, rotatorcuff repair or as suture plugs. Bone tissue can be used as whole orpartial bone replacement, bone plugs, bone screws or bone chips(including preparations in which bone chips can be prepared as a paste).Bone tissue can also be used for periodontal applications or as spinalspacers.

In a further embodiment, the hard and soft tissue from animals lackingany expression of functional alpha-1,3-galactosyltransferase can be usedin skin repair, for example, to repair deep tissue burns of the skin.Skin tissues include, but are not limited to, dermal or epidermal tissueor derivatives thereof.

In another aspect of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in internal tissue repair,such as abdominal wall repair, hernia repair, heart valve repair orreplacement, cosmetic surgery/repair, maxilofacial repair, for repair ofgynecological or urological tissues, and dura repair. Internal tissuesinclude pericardial tissue, heart valves and submucosal tissue. In oneembodiment, the submucosal tissue can be used to repair or replaceconnective tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting the relative lytic effects of complement oncells from fetuses 680B1-4.

FIG. 2 depicts a short segment of the coding region of the alpha-1,3-GTgene (see GenBank Acc. No. L36152) in which the point mutation selectedby Toxin A occurs. Upper sequence occurs in wild type; lower sequenceshows the change due to the point mutation in the second allele.

FIG. 3 is a representation of a 3-dimensional model of the UDP bindingsite of bovine alpha1,3GT. The aromatic ring of the tyrosine residue(foreground, white) can be seen in close proximity to the uracil base ofUDP (grayscale).

FIG. 4 is a photograph of homozygous, alpha-1,3-GT deficient cloned pigsproduced by the methods of the invention, born on Jul. 25, 2002.

FIG. 5 is a graph depicting Anti-alpha-1,3-gal IgM levels before andafter injections of piglet islet-like cell clusters (ICC) inalpha-1,3-GT KO mice. Each mouse received three serial ICC injectionsvia i.p. (200-500 ICC per injection) over 4 days. All three recipientsof wild-type (WT) piglet ICCs showed a significant elevation ofanti-alpha1,3Gal IgM titer and subsequent return to baseline 4 weeksafter ICC implants. Sera from all three mice injected with alpha-1,3-GTDKO piglet ICCs maintained low baseline values of anti-alpha-1,3-gal IgMtiter during the observation time of 35 days (Phelps et al., Science299: 411-414, 2003, figure S4).

FIG. 6 is a diagram of the porcine alpha-1,3-GT locus, corresponding toalpha-1,3-GT genomic sequences that can be used as 5′ and 3′ arms inalpha-1,3-GT knockout vectors, and the structure of the targeted locusafter homologous recombination. The names of names and positions of theprimers used for 3′PCR and long-range PCR are indicated by short arrows.The short bar indicates the probe used for alpha-1,3-GT Southern blotanalysis. The predicted size of Southern bands with BstEII digestion forboth the endogenous alpha-1,3-GT locus and the alpha-1,3-GT targetedlocus is also indicated.

FIG. 7 provides an overview of the anatomy of the knee. It shows a frontview of the right knee in a flexion position.

DETAILED DESCRIPTION

The present invention is tissue products from animals lacking anyexpression of functional alpha-1,3-galactosyltransferase for use asxenografts. The tissue can be hard tissue, such as bone, or soft tissue,such as dermal. This hard and soft tissue can be used forxenotransplantation, such as orthopedic reconstruction and repair, skinrepair and internal tissue repair. The animal can be a ruminant or anungulate, such as a bovine, porcine or ovine. In specific embodiment,the animal is a pig. The tissues from animals lacking any functionalexpression of the alpha-1,3-GT gene can be obtained from a prenatal,neonatal, immature, or fully mature animal, such as a porcine, bovine orovine.

In embodiments of the present invention, the alleles of the alpha-1,3-GTgene are rendered inactive, such that the resultant alpha-1,3-GT enzymecan no longer generate galactose alpha1,3-galactose on the cell surface.

The tissues from animals lacking any functional expression of thealpha-1,3-GT gene can be obtained from a prenatal, neonatal, immature,or fully mature animal, such as a porcine, bovine or ovine. In oneembodiment, the tissue can be used in its “native” form (directlyremoved from the animal). Alternatively, the tissue can be subjected tofurther treatment or modification.

In one embodiment of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in orthopedic reconstructionand repair. In a further embodiment, the hard and soft tissue fromanimals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in skin repair. In anotheraspect of the present invention, the hard and soft tissue from animalslacking any expression of functional alpha-1,3-galactosyltransferase canbe used in internal tissue repair.

Definitions

As used herein, the term “animal” (as in “genetically modified (oraltered) animal”) is meant to include any non-human animal, particularlyany non-human mammal, including but not limited to pigs, sheep, goats,cattle (bovine), deer, mules, horses, monkeys, dogs, cats, rats, mice,birds, chickens, reptiles, fish, and insects. In one embodiment of theinvention, genetically altered pigs and methods of production thereofare provided.

As used herein, an “organ” is an organized structure, which can be madeup of one or more tissues. An “organ” performs one or more specificbiological functions. Organs include, without limitation, heart, liver,kidney, pancreas, lung, thyroid, and skin.

As used herein, a “tissue” is an organized structure comprising cellsand the intracellular substances surrounding them. The “tissue” alone orin conjunction with other cells or tissues can perform one or morebiological functions. The tissue can be hard or soft tissue. A “tissueproduct” includes a tissue and/or a tissue fragment or tissue derivativethereof as described herein. This “tissue product” can be used toreplace or repair a human tissue. Such “tissue products” can bemodified, such as, but not limited to de-cellularized, according to themethods described herein.

As used herein, the terms “porcine”, “porcine animal”, “pig” and “swine”are generic terms referring to the same type of animal without regard togender, size, or breed.

As used herein the term prostheses or prosthetic device refers to a hardor soft tissue that has been crafted into an appropriate form for bodyrepair. In one embodiment, the body being repaired can be a human body.In other embodiments, the mammal body parts can be repaired, forexample, horses, dogs, cats or other domestic animals.

I. Types and Preparation of Tissue

The tissues from animal lacking any functional expression of thealpha-1,3-GT gene can be obtained from a prenatal, neonatal, immature,or fully mature animal, such as a porcine, bovine or ovine.

In one embodiment, the tissue can be used in its “native” form (directlyremoved from the animal). In an alternate embodiment, the tissue can besubjected to further treatment or modification. Tissues and the animalsource of the tissues can be further modified or treated to promotewound healing; minimize or eliminate unwanted pathogens, such asinfectious disease transmission (such as prions and retroviruses); addgrowth factors to promote tissue remodeling, sterilize the tissue,and/or improve the biomechanical or physical properties of the tissue.

In one embodiment, the type of treatment can be chemical, mechanical orphysical, such as enzymatic and/or exposure to a gas, ethylene oxidetreatment, propylene oxide treatment, gas plasma sterilization,peracetic acid sterilization, ultra violet radiation, or gammairradiation. The methods of the invention, include, alone or incombination, treatment with radiation, one or more cycles of freezingand thawing, treatment with a chemical cross-linking agent, treatmentwith alcohol or ozonation. When more than one of these treatments isapplied to the xenograft, the treatments may occur in any order.

In one embodiment, the xenograft tissue can be treated by exposure toultraviolet radiation, for example, exposure to ultraviolet radiationfor about fifteen minutes. In another embodiment, the tissue can beexposed to gamma radiation. The tissue can be exposed to gamma radiationin an amount of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 7.0,10, 15 or 20 MegaRad, or between about 0.5 to 3 or 1.5 to 2.0 MegaRad.In a further embodiment, the xenograft can be subjected to ozonation. Inother embodiments, the tissue can be treated according to acceptedstandards for sterilization, see for example, American NationalStandard, ANSI/AAMI/ISO 11137-1994, Sterilization of health careproducts—Requirements for validation and routine control—Radiationsterilization, 1994, American National Standard, ANSI/AAMI ST32-1991,Guidelines for Gamma Radiation Sterilization, 1991, Scholla, M. H. andWells, M. E. “Tracking Trends in Industrial Sterilization.” MedicalDevice and Diagnostic Industry, September 1997, pp. 92-95, AAMIRecommended Practice—“Process Control Guidelines for Gamma RadiationSterilization of Medical Devices,” ISBN No. 0-910275-38-6, pp. 7-21,1984, American National Standard, ANSI/AAMI/ISO 11137-1994,Sterilization of health care products-Requirements for validation androutine control-Radiation sterilization, 1994, American NationalStandard, ANSI/AAMI ST32-1991, Guideline for Gamma RadiationSterilization, 1991, American National Standard, ANSI/AAMI ST31-1990,Guideline for Electron Beam Radiation Sterilization of Medical Devices,1990, Genova, Hollis, Crowell and Schady, “A Procedure for Validatingthe Sterility of an Individual Gamma Radiation Sterilized ProductionBatch,” Journal of Parenteral Science and Technology, Volume. 41, No. 1,pp. 33-36, January 1987, and Gaughran and Morrissey, “Sterilization ofMedical Products,” Volume 2, ISBN-0-919868-14-2, pp. 35-39, 1980.

In another embodiment, the xenograft tissue can be treated immersion inan alcohol solution. Any alcohol solution can be used to perform thistreatment, including, but not limited to, primary alcohols, secondaryalcohols, tertiary alcohols, polyols, higher order alcohols, aromaticalcohols, such as phenol, heteroaromatic alcohols, ethanol, methanol,propanol, methyl-propanol, isopropyl alcohol, 2-propanol, cyclobutanol,1,2-ethanediol 4,4-dimethyl-2-pentanol, 4-penten-2-ol,4-amino-3-isopropylhexanol 5-mercapto-2,4-cyclohexadienol. The alcoholsolutions can be 10, 20, 30, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90,95, 96, 97, 98, or 99% alcohol. For example, a 70% solution ofisopropanol. The alcohol solution can be used at room temperature (suchas approximately 20-30° C., or 25° C.) or at low temperatures (such asapproximately 0-20° C.).

In a further embodiment, the xenograft tissue can be treated byfreeze/thaw cycling. For example, the xenograft tissue can be frozenusing any method of freezing. In one embodiment, the tissue iscompletely frozen, such that no interior warm spots remain which containunfrozen tissue. In one embodiment, the xenograft tissue can be immersedinto liquid nitrogen for a period of time. The tissue can be immersedfor about at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 15 minutes. Inanother embodiment, the xenograft can be frozen. For example, the tissuecan be placed in a freezer or by exposing the tissue to temperatures ator below 0° C. Then, in the next step of the freeze/thaw cyclingtreatment, the xenograft tissue can be thawed by immersion in ansuitable solution, for example, an isotonic saline bath. The temperatureof the bath can be approximately at room temperature, such as about 25°C. The tissue can be immersed in the saline bath for a period of timethat allows thawing, for example, at least 5, at least 10 or at least 15minutes. In other embodiments, the tissue can be treated withcryoprotectants prior to or during the freeze-thawing treatment.

In yet a further embodiment, the xenograft can be exposed to a chemicalagent to tan or crosslink the proteins within the extracellular matrix.Any tanning or crosslinking agent can be used for this treatment, andmore than one crosslinking step can be performed or more than onecrosslinking agent can be used to achieve a high degree of crosslinkingCross linking agents can act, for example, in the following ways: bycoupling an amine group on one biomolecule to a thiol group on a secondbiomolecule, forming crosslinks between amines of biopolymers, bycrosslinking amines and thiols, forming crosslinks between amines andcarboxylic acids or thiols and carboxylic acids.

In one embodiment, aldehydes, such as glutaraldehyde, formaldehyde,paraformaldehyde, formalin, aldehydes, adipic dialdehyde, tanning atacidic pH and the like, can be used to crosslink the collagen within theextracellular matrix of the tissue. In another embodiment, aliphatic andaromatic diamines, carbodiimides, diisocyanates, and other materialsknown by one skilled in the art can be used as crosslinking agents. Inone embodiment, the xenograft tissue can be treated with glutaraldehyde.For example, the tissue can placed in a buffered solution that cancontain at least 0.25, 0.5, 1, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8,9, 10, 15 or 20% or about 0.05 to about 5.0%; about 1-3% or about 2-7%glutaraldehyde. This solution can have a pH of about 7.4, 7.5 or 7.6.Any suitable buffer can be used, such as phosphate buffered saline ortrishydroxymethylaminomethane. In an alternative embodiment, thexenograft tissue can be treated with a crosslinking agent in a vaporform. In one embodiment, the crosslinking agent can be a vaporizedaldehyde crosslinking agent, such as, for example, vaporizedformaldehyde. In one embodiment, the tissue can be exposed to avaporized crosslinking agent at a concentration of at least 0.25, 0.5,1, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 15 or 20% or about0.05 to about 5.0%; about 1-3% or about 2-7%. In another embodiment, thepH of the vaporized crosslinking agent can be about 7.4, 7.5 or 7.6. Inanother embodiment, the tissue can be treated with a crosslinking agentfor at least 1, at least 2, at least 3, at least 4, at least 5, at least6, at least 7, at least 8, at least 9, at least 10, at least 11, atleast 12, at least 13, at least 14, at least 15 or at least 16 days. Inspecific embodiments, the tissue can be treated with a crosslinkingagent for 3, 4 or 5 days.

Cross linking agents can also be selected from the group including, butnot limited to: dithiothreitol (DTT, D-1532),tris-(2-carboxyethyl)phosphine (TCEP, T-2556)tris-(2-cyanoethyl)phosphine (T-6052). succinimidyl3-(2-pyridyldithio)propionate (SPDP, S-1531), succinimidylacetylthioacetate (SATA, S-1553), mercaptotryptophan, SPDP/DTT incombination, SPDP/TCEP in combination, dibromobimane (D-1379), BODIPY FLbis-(methyleneiodoacetamide) (D-10620),bis-((N-iodoacetyl)piperazinyl)sulfonerhodamine (B-10621), bis(imidoesters), bis(succinimidyl esters), diisocyanates, diacid chlorides.bis-(4-carboxypiperidinyl)sulfonerhodamine, di(succinimidyl ester)(B-10622), 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC, E-2247),succinimidyl ester of 6-((acryloyl)amino)hexanoic acid (acryloyl-X, SE;A-20770), and streptavidin acrylamide (S-21379, Section 7.5).

In another embodiment, the tissues from animals lacking any functionalexpression of the alpha-1,3-GT gene can be combined with other inertmaterials such as plastics, biopolymers, and metals (including but notlimited to stainless steel and titanium) in order to provide additionalmechanical strength or for other application benefits to the recipientpatient. Biopolymers include, but are not limited to cellulose, alginicacid, chitosan, collagen, elastiri, and reticulin and analogs thereof,and mixtures thereof.

In other embodiments, the prostheses can further include syntheticmaterials, such as polymers and ceramics. Appropriate ceramics include,for example, hydroxyapatite, alumina, graphite and pyrolytic carbon.Appropriate synthetic materials include hydrogels and other syntheticmaterials that cannot withstand severe dehydration. The xenografts canalso contain synthetic polymers as well as purified biological polymers.These synthetic polymers can be woven or knitted into a mesh to form amatrix or similar structure. Alternatively, the synthetic polymermaterials can be molded or cast into appropriate forms.

Appropriate synthetic polymers include without limitation polyamides(e.g., nylon), polyesters, polystyrenes, polyacrylates, vinyl polymers(e.g., polyethylene, polytetrafluoroethylene, polypropylene andpolyvinyl chloride), polycarbonates, polyurethanes, poly dimethylsiloxanes, cellulose acetates, polymethyl methacrylates, ethylene vinylacetates, polysulfones, nitrocelluloses and similar copolymers.Bioresorbable polymers can also be used such as dextran, hydroxyethylstarch, gelatin, derivatives of gelatin, polyvinylpyrolidone, polyvinylalcohol, poly[N-(2-hydroxypropyl)methacrylamide], poly(hydroxy acids),poly(epsilon-caprolactone), polylactic acid, polyglycolic acid,poly(dimethyl glycolic acid), poly(hydroxy buterate), and similarcopolymers. These synthetic polymeric materials can be woven or knittedinto a mesh to form a matrix or substrate. Alternatively, the syntheticpolymer materials can be molded or cast into appropriate forms.

Biological polymers can be naturally occurring or produced in vitro byfermentation and the like or by recombinant genetic engineering.Recombinant DNA technology can be used to engineer virtually anypolypeptide sequence and then amplify and express the protein in eitherbacterial or mammalian cells. Purified biological polymers can beappropriately formed into a substrate by techniques such as weaving,knitting, casting, molding, extrusion, cellular alignment and magneticalignment. Suitable biological polymers include, without limitation,collagen, elastin, silk, keratin, gelatin, polyamino acids,polysaccharides (e.g., cellulose and starch) and copolymers thereof.

In one embodiment, the tissue can be used as a complete tissuereplacement, such that, for example, the transplanted tissue performsthe same biomechanical functionality of the tissue it is replacing orrepairing. In a further embodiment, the tissue can be preconditioned(chemically and/or mechanically) prior to transplantation to allowoptimal range of motion of the tissue following transplantation, or toallow for a “custom fit” for the recipient. In further embodiments, thetissue can be further treated and/or processed as described below toform de-cellularized products, which can be used, for example, asscaffold, once implanted.

A. Tissue Reconstruction, Repair and/or Replacement

In one embodiment of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used for surgical applications.In one embodiment, the tissue can be used in orthopedic reconstructionand repair. Such tissues include soft tissue, such as connective tissue,tendons, ligaments, muscle and cartilage as well as hard tissue, such asbone and bone derivatives. In one embodiment, the tissue can be used forknee repair, such as anterior cruciate ligament (ACL) or posteriorcruciate ligament (PCL) replacement. In another embodiment, the tissuecan be used for bone-tendon-bone grafts, rotator cuff repair or assuture plugs. Bone tissue can be used as whole or partial bonereplacement, bone plugs, bone screws or bone chips (includingpreparations in which bone chips can be prepared as a paste). Bonetissue can also be used for periodontal applications, cosmetic, and/ormaxilofacial reconstruction. Tissue can also be used as spinal spacersfor vertebrae repair. Tissue can also be used to replace tissue of theear, such as ossicles, tympanic membranes, tympanic membranes withmallei attached, ear bone plugs, temporal bones, costal cartilage anddura mater), which can optionally be used for inner ear reconstruction.

1. Bone Tissue

In one embodiment, the invention provides a method of preparing a bonexenograft for implantation or engraftment into a human, which includesremoving at least a portion of a bone or a whole piece of bone from ananimal to provide a xenograft.

The bone can be harvested from any non-human animal to prepare thexenografts of the invention. In one embodiment, the bone can be obtainedfrom bovine, ovine, or porcine animals. In another embodiment, the boneis obtained from immature pigs, calves or lambs. The bone of youngeranimals consists of more cancellous bone and is generally less brittlethan that of older animals. In another embodiment, the bone is obtainedfrom an animal between six and eighteen months of age.

An intact bone portion can be removed from a bone of the animal. Thebone can be collected from freshly killed animals. Alternatively, thebone can be surgically removed from viable animals. Bones that areremoved can include, but are not limited to, skull bone, such asanterior, lateral or posterior; vertebrae, such as cervical (atlas,axis, typical), thoracic (superior, inferior) lumbar (superior inferiorlateral), sacrum, pelvis, thorax, sternum, rib, upper extremity bone,scapula, ventral, dorsal, clavicle, humerus (anterior or) posterior,radius-ulna (anterior or posterior), hand (dorsal or palmar), femur(anterior or posterior), tibia-fibula (anterior or posterior) and/orfoot (dorsal or lateral). In one embodiment, after removal, the bone canbe placed in a suitable sterile isotonic or other tissue preservingsolution. Harvesting of the bone portions after slaughter of the animalcan be done as soon as possible after slaughter and can be performed atcold temperature. For example, between about 5° C. and about 20° C.,about 0° C. and about 20° C., about 0° C. and about 10° C., or about 0°C. and about 25° C.

The xenograft tissue, can then be washed in sterile, optionally cold,water to remove residual blood proteins and water soluble materials. Inone embodiment, the xenograft tissue can then be immersed in alcoholunder conditions such as those described above. The xenograft can besubjected to chemical, mechanical or biological treatments, such asthose described above.

In one embodiment, the harvested bone portion can be cut up into stripsor blocks. In another embodiment, the harvested bone can be made intoany useful configuration of a bone graft, including, but not limited to,bone dowels, spinal spacers, bone plugs, bone chips, bone screws, bonecement, D-shaped spacers and cortical rings. The strips, blocks or otherbone grafts can be created such that cancellous bone is attached tocortical bone. Alternatively, strips, blocks or other bone grafts can becreated such that cancellous bone is not attached to cortical bone.

Bone Cement and Bone Plugs

In other embodiments of the present invention, bone cement and boneplugs from animals lacking any expression of functional alpha-1,3-GT areprovided.

Bone cement compositions are useful in the bonding or fixing of animplant material, as well as in the strengthening of damaged naturalbone. Such applications are useful in the areas of, for example,orthopedics, dentistry and related medical disciplines. The field oforthopedics deals with bone defects due to fracture, bone tumors, andother diseases of the bone. Treatment may require surgical resection ofall, or part, of a bone. In dentistry applications, a defected jawbonemay result from extraction of a tooth, cancer or other diseases. Animplant material is useful in repairing or reconstructing the boneremaining after the resection of such bone defects. Implant materialsused during such procedures can be metal, ceramics and polymers. Bonecement can be used in addition to other implant material to bond andaffix the implant to the remaining, living bone. For example, polymethylmethacrylate (PMMA) has been widely used with hardware instrumentationin orthopedics.

Although conventional PMMA bone cement has been used in orthopedicsurgery for over 40 years, it is far from ideal because 1) it does notencourage bone in-growth, 2) it is a weaker implement than bone cortex,and 3) it has a high exotherm and monomer toxicity. Thus, the presentinvention provides matrix materials, such as those described herein,that can be formulated into bone cement. Such bone cement can exhibitquick hardening time and/or chemically bonds, to affix an artificialbiomaterial (e.g., implant material). This cement can display in vivobioactivity, maintain mechanical strength, be characterized by adequatestiffness and modulus and/or improves bone mass through its physical andchemical effects. The bone cement can include a powder and liquidcomponent. In one embodiment, the bioactive bone cement is provided in apowder-liquid phase, comprising a powder phase material and a liquidphase material. In another embodiment, the bioactive bone cement isprovided in a paste-paste phase, comprising two separate pastematerials. Additionally, the bone cement materials provided herein canbe combined with other types of bone cement components, such as, PMMAbone cement. The bone cement can be used in any conventional manner,such as through injection via a syringe. The bone cement of the presentinvention can be used, for example, in spinal surgery via injection witha syringe. Syringe injection provides a minimally invasive deliverytechnique via the use of a syringe and a large bore needle. It alsoallows the cement to conform precisely to its area of placement.Additionally, the bone cement or paste can be combined with growthfactors or cytokines, including but not limited to, bone morphogenicproteins (BMPs).

Bone plugs can be used for permanent or temporarily blocking of a canalin a long bone. For fixating of an endoprosthesis or artificial joint,for example an artificial hip prosthesis, in a bone, a stem of theprosthesis is inserted in the intramedullary canal of a long bone whichis filled with bone cement. In order to prevent the bone cement toprotrude in the canal any further than necessary for fixating of thestem and to assure that the bone cement is only present between the stemand the endosteal wall of the bone and to prevent leaking of the bonecement any further into the intramedullary canal, the canal beneath thestem is blocked with a bone plug. (see, for example, U.S. Pat. Nos.6,669,733, 6,494,883).

Bone plugs can be molded in a wide range of sizes and having variousheight-to-diameter ratios in order to accommodate a wide range ofcartilage replacement situations. The bone plug can be a polygonal orcircular cross-section. For example, the plug can be a round deviceshaving a shape ranging from flat disks to cylinders. A variety offactors can be taken into consideration for each particular application,such as the location where the bone replacement plug or plugs are to beimplanted, the size of the bone defect that is to be repaired, and thesize and shape of the void cavity, either as initially formed byresection of the defect, or by any subsequent surgical contouring of thecavity, into which the cartilage replacement plug is to be implanted.

Bone cement plugs can also be used, such devices are well known in theart. Bone cement plugs can be used in conjunction with bone cementdispensers to compact bone cement into a bone canal before fixing aprosthetic device in that bone canal. By way of example, bone cementplugs can be used in conjunction with bone cement despensers to compactbone cement into the intramedullary canal of the femur before fixing thefemoral stem of an artificial hip in that canal. More particularly, intotal joint replacement surgeries, such as hip and shoulderreplacements, bone cement can be used to fix the stems of the prostheticdevices into the medullary canals of the joint's bones. In thcan berespect, it has generally been found that a prosthetic device will bemore securely fixed in a bone canal if the bone cement can be wellpacked into the bone canal before the stem of the prosthetic device ispositioned in the bone canal. In one example, after initial preparationand cleaning of the bone canal, the distal portion of the canal can begenerally occluded with a plug. The bone cement plug can serve to limituncontrolled flow of bone cement into the distal portion of the bonecanal. In one specific embodiment, the bone cement plug can limit thecolumn of bone cement to about 1 to 2 cm beyond the distal tip of thestem of the prosthesis. After the plug has been set at the distalportion of the bone canal, the bone cement can be injected into thedistal-most part of the occluded bone canal, adjacent to the plug, usinga bone cement dispenser having a long nozzle. The bone canal can be thenfilled with bone cement in a retrograde fashion, by withdrawing thenozzle of the bone cement dispenser from the distal end of the bonecanal to the proximal end of the bone canal, as the cement issues fromthe nozzle. Such retrograde filling can help to avoid trapping air inthe distal-most part of the bone canal. After the bone canal has beenfilled with bone cement, a bone canal pressurizer can then be connectedto the bone cement dispenser. The pressurizer can be pressed against theopen end of the bone so as to occlude the proximal end of the bonecanal. More cement can be then injected into the bone canal through thepressurizer and under pressure. Under such pressurization, the cement inthe bone canal intrudes into the interstices of the inner surface of thebone wall defining the bone canal. When the bone cement thereafter sets,a micro-interlock can be established between the cement and theirregularities of the inner surface of the bone wall. This cansignificantly enhance fixation of the prosthetic device in the bonecanal.

In one embodiment, the bone cement plug can be easy to deploy at thedesired depth in the bone canal, effective in closing off that bonecanal and, in the event that the bone cement plug subsequently needs tobe removed, easy to retrieve from the distal end of the bone canal.

A variety of bone cement plugs are known in the art. See, for example,U.S. Pat. Nos. 4,245,359; 4,276,659; 4,293,962; 4,302,855; 4,344,190;4,447,915; 4,627,434; 4,686,973; 4,697,584; 4,745,914; 4,936,859;4,950,295; 4,994,085; 5,061,287; 5,078,746; 5,092,891; 5,376,120;4,011,602; 4,523,587; 4,904,267, 6,299,642, 6,306,142 and 5,383,932, andWO 94/15544.

Surgical techniques for transplanting bone plugs can involve removingthe damaged bone tissue by drilling or cutting a hole at the site of thedamage, and plugging this hole with a bone plug. Surgical instrumentscan be used to harvest or extract a bone plug from a donor site from ananimal lacking any expression of functional alpha-1,3-GT. The bone plugcan then be implanted it into a pre-formed hole at a recipient site. Aconventional harvesting instrument can include a tube having a cuttingedge at the distal end. To extract the plug, the instrument can bedriven into the bone at the donor site and then removed, taking with ita plug of bone tissue.

Bone Screws

In another embodiment, bone screws derived from animals lacking anyexpression of functional alpha-1,3-GT are provided.

One method of reducing bone fractures can be to use external fixationdevices which allows fractures to be consolidated to highly criticalareas, as may be especially those proximate to joints, or fracturesinvolving serious damage to the cutaneous tissue to be treated, that is,anywhere traditional plastering may prove inappropriate orimpracticable. Such devices, usually of complex construction andsupplied in varying configurations for adaptation to the mostunpredictable of contingent situations, have opposite ends which arefastened to respective undamaged portions of the broken bone, usingscrews firmly set in the bone material of these portions. Thus, forexample in the case of a tibial fracture, the opposite ends of acorresponding (tibial) fixation device are secured across the fracturedregion. In other cases, where the fracture involves a joint such as anankle, the bone screws of a corresponding external fixation device areset in the shinbone and the talus.

Bone screws for fastening the external fixation device, and thusensuring the device effectiveness, can include a screw head designed forengagement by a suitable driver, and a screw shank having a threadedportion which usually tapers toward a screw tip at the opposite end fromsaid head. The screw head can be formed with a flat which extendsparallel to the screw axis, milled on one side of the screw shank. Bonescrews can be on varying lengths such that the screw is suitable for theparticular size and shape of bone into which it can be inserted.

Spinal Spacers

In other embodiments of the present invention, any component of thespine from animals lacking any expression of functional alpha-1,3-GT areprovided. Such components include, but are not limited to, spinalspacers, intervertebral discs, the nucleus pulposus and/or the annulusfibrosis.

Spinal fusion is indicated to provide stabilization of the spinal columnfor painful spinal motion and disorders such as structural deformity,traumatic instability, degenerative instability, and post-resectioniatrogenic instability. Fusion, or arthrodesis, is achieved by theformation of an osseous bridge between adjacent motion segments. Thiscan be accomplished within the disc space, anteriorly between contiguousvertebral bodies or posteriorly between consecutive transverseprocesses, laminae or other posterior aspects of the vertebrae. Asuccessful fusion requires the presence of osteogenic or osteopotentialcells, adequate blood supply, sufficient inflammatory response, andappropriate preparation of local bone.

A fusion or arthrodesis procedure can be performed to treat an anomolyinvolving an intervertebral disc. Intervertebral discs, located betweenthe endplates of adjacent vertebrae, stabilize the spine, distributeforces between vertebrae and cushion vertebral bodies. A normalintervertebral disc includes a semi-gelatinous component, the nucleuspulposus, which is surrounded and confined by an outer, fibrous ringcalled the annulus fibrosis. In a healthy, undamaged spine, the annulusfibrosis prevents the nucleus pulposus from protruding outside the discspace.

Spinal discs can be displaced or damaged due to trauma, disease oraging. Disruption of the annulus fibrosis allows the nucleus pulposus toprotrude into the vertebral canal, a condition commonly referred to as aherniated or ruptured disc. The extruded nucleus pulposus may press onthe spinal nerve, which may result in nerve damage, pain, numbness,muscle weakness and paralysis. Intervertebral discs may also deterioratedue to the normal aging process or disease. As a disc dehydrates andhardens, the disc space height will be reduced leading to instability ofthe spine, decreased mobility and pain. One treatment for theseconditions is a discectomy, or surgical removal of a portion or all ofan intervertebral disc followed by fusion of the adjacent vertebrae. Theremoval of the damaged or unhealthy disc can allow the disc space tocollapse. Collapse of the disc space can cause instability of the spine,abnormal joint mechanics, premature development of arthritis or nervedamage, in addition to severe pain. Pain relief via discectomy andarthrodesis requires preservation of the disc space and eventual fusionof the affected motion segments.

Bone grafts or spinal spacers can be used to fill the intervertebralspace to prevent disc space collapse and promote fusion of the adjacentvertebrae across the disc space. Many attempts to restore theintervertebral disc space after removal of the disc have relied on metaldevices (see, for example, U.S. Pat. Nos. 4,878,915, 5,044,104;5,026,373, 4,961,740; 5,015,247, 5,147,402 and 5,192,327)

Spinal components from animals lacking expression of functionalalpha-1,3-GT can be prepared according to conventional methods. The bonecan be obtained from the animal and then cleaned to remove tissue andblood. The bone can be treated with agents, such as alcohol andperoxides or other agents as described above, to remove cellularmaterial, fats and noncollagenous proteins. The bone material can betreated to remove free collagen, leaving bound or structural collagen.One agent for removing free collagen and any remaining fat is sodiumdodecyl sulfate (SDS).

2. Soft Tissue

Soft tissue connects, supports or surrounds other structures and organsof the body. Soft tissue includes, for example, muscles, tendons, fat,blood vessels, lymph vessels, nerves, tissue around the joints skin orany other tissue other than bone.

Soft tissues, such as such as connective tissue, tendons, meniscus,ligaments, muscle and cartilage can be extracted from a joint of ananimal. The source of the tissue can be collected from freshly killedanimals. Alternatively, the tissue can be surgically removed from viableanimals. Any joint can serve as the source of the soft tissue. Inembodiments of the invention, tissue from a corresponding donor jointcan be used to make the xenograft tissue. For example, cartilage from afemuro-tibial (stifle) joint can be used to make a cartilage xenograftfor implantation into a knee. In another example, cartilage from a donoranimal's hip joint can be used to make a cartilage xenograft for a humanhip joint.

In one embodiment, the soft tissue can be extracted from the knee joint.The knee is a complex joint containing spatially interrelated bones,ligaments, and cartilaginous structures which interact to create avariety of motions. Specifically, the femoral condyles articulate withthe surface plateaus of the tibia, through the cartilaginous medial andlateral menisci, and all of these structures are held in place byvarious ligaments. There are essentially four separate ligaments thatstabilize the knee joint (see, for example, FIG. 7). On the sides of thejoint lie the medial collateral ligament (MCL) and the lateralcollateral ligament (LCL) which serve as stabilizers for theside-to-side stability of the joint. The MCL is a broader ligament thatis actually made up of two ligament structures, the deep and superficialcomponents, whereas the LCL is a distinct cord-like structure. In thefront part of the center of the joint is the anterior cruciate ligament(ACL). This ligament is a very important stabilizer of the femur on thetibia and serves to prevent the tibia from rotating and sliding forwardduring agility, jumping, and deceleration activities. Directly behindthe ACL is its opposite, the posterior cruciate ligament (PCL). The PCLprevents the tibia from sliding to the rear.

The medial and lateral menisci are structures comprised of cells calledfibrochondrocytes, an interstitial matrix of fibers of the proteincollagen, and within a ground substance formed from proteoglycans.Undamaged menisci provide shock absorption for the knee by ensuringproper force distribution, stabilization, and lubrication for theinteracting bone surfaces within the knee joint, which are routinelyexposed to repeated compression loading during normal activity. Much ofthe shock absorbing function of the medial and lateral menisci isderived from the elastic properties inherent to cartilage. When menisciare damaged through injury, disease, or inflammation, arthritic changesoccur in the knee joint, with consequent loss of function.

The anterior cruciate ligament of the knee (the ACL) functions to resistanterior displacement of the tibia from the femur at all flexionpositions. The ACL also resists hyperextension and contributes torotational stability of the fully extended knee during internal andexternal tibial rotation. The ACL may play a role in proprioception. TheACL is made up of connective tissue structures composed of cells, water,collagen, proteoglycans, fibronectin, elastin, and other glycoproteins(see, for example, Cyril Frank, M. D. et al., Normal Ligament:Structure, Function, and Composition. Injury and Repair of theMusculoskeletal Soft Tissues, 2:45-101). Structurally, the ACL attachesto a depression in the front of the intercondyloid eminence of the tibiaextending postero-superiorly to the medial wall of the lateral femoralcondyle. Partial or complete tears of the ACL are very common,comprising about 30,000 outpatient procedures in the U.S. each year.

Articular cartilage covers the ends of all bones that form articulatingjoints in humans and animals. The cartilage is made of cells calledfibrochondrocytes and an extracellular matrix of collagen fibers as wellas a variety of proteoglycans. The cartilage acts in the joint as amechanism for force distribution and as a lubricant in the area ofcontact between the bones. Without articular cartilage, stressconcentration and friction would occur to the degree that the jointwould not permit ease of motion. Loss of the articular cartilage usuallyleads to painful arthritis and decreased joint motion. Since jointcartilage in adults does not naturally regenerate to a significantdegree once it is destroyed, damaged adult articular cartilage hashistorically been treated by a variety of surgical interventionsincluding repair, replacement, or by excision.

In one embodiment, meniscal soft tissue can be extracted from a joint byfirst transecting the patellar tendon, the horns of the menisci can thenbe dissected free of adhering tissue. Optionally, a small amount of bonecan remain attached to the horns, for example, a substantiallycylindrical plug of bone, such as a bone plug. In one specific example,the bone plug can be approximately five millimeters in diameter by fivemillimeters in depth. In one embodiment, the meniscal synovial junctioncan then be identified and freed from the meniscus tissue itself, toform a matrix material. In another embodiment, the intact meniscal softtissue can be used for transplantation.

In another embodiment, articular cartilage soft tissue can be extractedfrom a joint. In one embodiment a fine peel of articular cartilage witha small layer of subchondral bone can be identified and shaved from thedonor joint, this can form matrix material. In another embodiment, theintact articular cartilage soft tissue can be used for transplantation.

In a further embodiment, ligament soft tissue can be extracted from ajoint, such as the anterior cruciate ligament, posterior cruciateligament, lateral collateral ligament or the medial collateral ligament.To remove the ligament, the joint can be opened using standard surgicaltechniques. In one embodiment, the ligament can be harvested with ablock of bone attached to one or both ends. In one example, a block ofbone representing a substantially cylindrical plug can be extracted withthe ligament, the bone plug can be approximately 9-10 mm in diameter byapproximately 20-40 mm in length. In another embodiment, the ligament isharvested without bone. In a further embodiment, the ligament can beharvested without bone and then dissected free of adhering tissue toobtain a matrix material. In another embodiment, the intact ligamentsoft tissue can be used for transplantation.

After removal, the tissue can be placed in a suitable sterile isotonicor other tissue preserving solution. Harvesting of the tissue afterslaughter of the animal can be done as soon as possible after slaughterand can be performed at cold temperature. For example, between about 5°C. and about 20° C., about 0° C. and about 20° C., about 0° C. and about10° C., or about 0° C. and about 25° C.

Collagen

In another embodiment, collagen tissue of the present invention can beused to treat collagen disorders. Alterations in collagen structureresulting from abnormal genes or abnormal processing of collagenproteins results in numerous diseases, such as Larsen syndrome, scurvy,osteogenesis imperfecta and Ehlers-Danlos syndrome. Ehlers-Danlossyndrome is actually the name associated with at least ten distinctdisorders that are biochemically and clinically distinct yet allmanifest structural weakness in connective tissue as a result of defectsin the structure of collagens. Osteogenesis imperfecta also encompassesmore than one disorder. At least four biochemically and clinicallydistinguishable disorders have been identified all of which arecharacterized by multiple fractures and resultant bone deformities.Marfan's syndrome manifests itself as a disorder of the connectivetissue and was believed to be the result of abnormal collagens. However,recent evidence has shown that Marfan's results from mutations in theextracellular protein, fibrillin, which is an integral constituent ofthe non-collagenous microfibrils of the extracellular matrix.

TABLE 3 Collagen Disorders Disorder Collagen Defect SymptomologyEhlers-Danlos IV decrease in type III arterial, intestinal and uterinerupture, thin easily bruised skin Ehlers-Danlos V decreased skin andjoint hyperextensibility cross-linking Ehlers-Danlos VI decreased poorwound healing, musculo- hydroxylysine skeletal deformities, skin andjoint hyperextensibility Ehlers-Danlos VII N-terminal easily bruisedskin, hip pro-peptide dislocations, hyperextensibility not removedOseteogenesis decrease in type I blue sclerae, bone deformitiesimperfecta Scurvy decreased poor wound healing, deficient hydroxyprolinegrowth, capillary weakness

Cartilage Plugs

In other embodiments, cartilage plugs are provided that are obtainedfrom animals lacking expression of functional alpha-1,3-GT. Cartilageplugs can be used to fill a void in natural cartilage. Voids in naturalcartilage can be due to traumatic injury or chronic diseaseAlternatively, the plug can be used to anchor a flowable polymer tosubchondral bone. The plug can be made into any size, shape, and contourthat is appropriate for the desired transplant. The plugs can beutilized either singly or in a plurality to fill any size void for anyapplication. The plug can be formed of or also include a laminatedstructure to match the physiological requirements of the repair site.Additionally, ridges can be formed about the periphery of each plug tofacilitate its anchoring to surrounding cartilage, bone and/or adjacentplugs (see, for example, U.S. Pat. No. 6,632,246).

The cartilage plug can be a polygonal or circular cross-section. Thepolygonal or circular cross-section can encompass a height-to-diameterratio of from about less than one to one to about 20:1, about 30:1 orabout 40:1. The plugs can be molded in a wide range of sizes and havingvarious height-to-diameter ratios in order to accommodate a wide rangeof cartilage replacement situations. For example, the plug can be around devices having a shape ranging from flat disks to cylinders. Avariety of factors can be taken into consideration for each particularapplication, such as the location where the cartilage replacement plugor plugs are to be implanted, the size of the cartilage defect that isto be repaired, and the size and shape of the void cavity, either asinitially formed by resection of the defect, or by any subsequentsurgical contouring of the cavity, into which the cartilage replacementplug is to be implanted. For example, cartilage replacement plug devicesthat have a flattened, disk shape are most suitable for more extensivebut shallow defects, while devices having a large height-to-diameterratio are suitable for defects having a smaller surface area, but whichextend deeper into the cartilage and/or the subchondral bone layer.

The surfaces of the cartilage plugs of the present invention can betreated so as to expose a porous or roughened surface. By treating thesurface of the plug such that it is roughened or textured, cellattachment can be enhanced and allows for cell migration and overgrowthof a tissue layer. With appropriate surface asperity, the resultantcells can adhere via ongrowth and ingrowth into the surface of the plugenhancing fixation. Such cell ingrowth can be ultimately transformedinto a bony interface with the plug and is considered a desirablecharacteristic. Important in this transformation is how load istransferred from the device to the surrounding tissue. A large mismatchin deformation between the plug and surrounding tissue can lead to afibrous tissue layer around the plug that, although flexible, does notprovide the desired fixation. Porosity, like asperity, can be importantand beneficial when considering biologic fixation.

Suture Anchors

Soft tissue provided in the present invention can be used to form sutureanchors, which can be used to secure sutures within openings formed inbones during joint reconstructive surgery and arthroscopic surgicalprocedures. The anchor can be placed in a bone and connected to a suturethat could otherwise not be secured to dense osseous material.

Such suture anchors can be used, for example, to anchor ligaments ortendons to bones in knee, shoulder and elbow reconstruction and repairoperations. Important attributes of bone anchors are that they be easyto insert, and provide a firm anchor. Unintended dislodgement of theanchor after surgery can have serious adverse consequences, hence muchimportance is placed on the ability of an anchor to resist extraction orwithdrawal forces exerted by the attached suture. (see, for example,U.S. Pat. Nos. 4,738,255, 4,013,071, 4,409,974, 4,454,875, and5,236,445)

The present invention also provides methods of anchoring a suture to abone. First a bore hole can be drilled in the bone. The bone anchor canthen be inserted, distal end first, into the bore hole. An expansioninstrument, such as a rod with an oblong or oval cross-section, can beinserted into the expansion chamber through the open proximal end of theanchor. The slotted proximal end of the bone anchor is then expanded byrotating the instrument to bring the instrument into contact with thewalls as the instrument rotates. The oblong or oval cross-section of theinstrument permits it to rotate through at least a portion of arevolution before contacting the walls, such that the bone anchor isless likely to rotate with the instrument. In one embodiment, the distaltip of the instrument seats in a corresponding recess at the distal endof the expansion chamber. The recess provides a fixed pivot point aboutwhich the rod rotates to expand the anchor.

3. Scaffolds

In certain embodiment, processes to prepare tissue can include steps tostrip away or kill all viable cells (decellularization) leaving behindonly an acellular matrix or scaffold for use in tissue repair andremodeling, as well as, optionally, treatments for crosslinking andsterilization. In a particular embodiment, any decellularized hard orsoft tissue is provided that is derived from the animals disclosedherein. In one embodiment, de-cellularized soft dermal tissue isprovided. In another embodiment, de-cellularized submucosal tissue isprovided. In other embodiment, such de-cellularized material can be lessimmunogenic. In further embodiments, such de-cellularized tissues can beused as a scaffolding or matrix to repair and/or reconstruct particularhuman body parts. In one embodiment, the decellularized tissue can beused for the repair of the following, including, but not limited to,hernia, abdominal wall, rotator ciff, cosmetic surgery or any other softtissue defects known to one skilled in the art or disclosed herein. Inparticular embodiments, submucosal and or dermal decellularized materialis provided.

In one aspect of the present invention, tissues derived from these alpha1,3GT animals can be procured (harvested) and then further processed toform de-cellularized tissue, for example, for use as scaffolds. In oneembodiment, the tissue can be subject to a multi-step process including,but not limited to, treating the tissue with a stabilizing solution, adecellularization process to remove cells and any remaining antigenictissue components, enzymatic treatment, cross-linking to improvestructural integrity of the tissue or to remove any remaining antigenictissue components, sterilization to remove and/or inactivate nativevirus, and/or long term preservation methods. In one embodiment, thestabilizing solution can contain an appropriate buffer, one or moreantioxidants, one or more oncotic agents, an antibiotic, and may includeone or more protease inhibitors.

In other embodiments, the tissue processing to produce de-cellularizedtissue can include, for example, removal of cells that can lead totissue rejection and graft failure, without damaging the matrix. Theprocess of decellularization has the advantage of rendering the tissueas strong as synthetics, yet more pliable, retaining tensile andfunctional characteristics, helping to prevent adhesions, decreasedinfection and rejection of the graft, and promoting remodeling of thesurrounding host tissue. In other embodiments, decellularization can beaccomplished using a number of chemical treatments, including incubationin certain salts, detergents or enzymes, and/or a vacuum/pressureprocess. In one embodiment, the detergent can be Triton X-100 (Rohm andHaas Company of Philadelphia, Pa.). In a certain embodiment, the TritonX-100 remove cellular membranes, see, for example, U.S. Pat. No.4,801,299. Other decellularizing detergents include, but are not limitedto, polyoxyethylene (20) sorbitan mono-oleate and polyoxyethylene (80)sorbitan mono-oleate (Tween 20 and 80), sodium deoxycholate,3-[(3-chloramidopropyl)-dimethylammino]-1-propane-sulfonate,octyl-glucoside and/or sodium dodecyl sulfate or any other detergentknown to one skilled in the art. In another embodiment, enzymes can beused to accomplish decellularization. In certain embodiments, theenzymes can be selected from the group including, but not limited todispase II, trypsin, and/or thermolysin or any other enzyme known to oneskilled in the art. These enzymes can react with different components ofcollagen and intercellular connections. For example, dispase II canattack Type IV collagen, which is a component of the lamina densa andanchoring fibrils of the basement membrane. In another example,thermolysin can attack the bulbous phemphigoid antigen in thehemidesmosome of the basal layer of keratinocytes. In a further example,trypsin can attack the desmosome complex between cells.

In additional or alternative embodiments, the de-cellularized xenograftcan be exposed to a chemical agent to tan or crosslink the proteinswithin the extracellular proteins, to further diminish or reduce theimmunogenic determinants present in the xenograft. Any tanning orcrosslinking agent may be used for this treatment, and more than onecrosslinking step can be performed or more than one crosslinking agentmay be used in order to ensure complete crosslinking and thus optimallyreduce the immunogenicity of the xenograft. For example, aldehydes suchas glutaraldehyde, formaldehyde, adipic dialdehyde, and the like, can beused to crosslink the extracellular collagen. Other suitablecrosslinking agents include aliphatic and aromatic diamines,carbodiimides, diisocyanates, and the like. Alternatively, the xenograftcan be exposed to a crosslinking agent in a vapor form, including, butnot limited to, a vaporized aldehyde crosslinking agent, such as, forexample, vaporized formaldehyde. The crosslinking reaction shouldcontinue until the immunogenic determinants are substantially removedfrom the xenogeneic tissue, but the reaction should be terminated priorto significant alterations of the mechanical properties of thexenograft. The cross-linking agents can be any agents known to oneskilled in the art or described herein.

In certain embodiments, matrix material derived from such soft tissuecan be used to form a scaffold or prosthetic device. The matrix materialcan be converted into a dry, porous volume matrix, a portion of whichcan optionally be cross-linked. The porous matrix of the prostheticdevice encourages ingrowth of cells, such as meniscal fibrochondrocytes,endothelial cells, fibroblasts, and other cells that normally occupy theextracellular matrix as well as synthesize and deposit extracellularmatrix components. Extracellular matrix fibers, such as collagen,elastin, reticulin, analogs thereof and mixtures thereof, can be addedto the matrix material. These fibers can also be obtained from animalslacking any functional expression of alpha-1,3-gal. In one embodiment,the fibers can be randomly oriented throughout the matrix.Alternatively, the fibers can assume substantially circumferentiallyextending or substantially radially extending orientation throughout thematrix. The density of the fibers of the matrix can be uniform ornon-uniform. In non-uniform configurations, relatively high densities offibers can be established at anticipated points of high stress.

The matrix materials can also contain other types of materials, such asbiopolymers as described above. The matrix material can containglycosaminoglycan molecules (GAGs), such as, but are not limited to,chondroitin 4-sulfate, chondroitin 6-sulfate, keratan sulfate, dermatansulfate, heparan sulfate, hyaluronic acid, and mixtures thereof can becomponents of the matrix material. In addition, the matrix material cancontain GAGs interspersed throughout the fibers. The GAGs can beuniformly dispersed throughout the matrix as individual molecules, orthey can be present in varying amounts in different regions of thedevice.

In another embodiment, the scaffolds formed from tissues from animallacking any functional expression of the alpha-1,3-GT gene as describedherein can also contain extracellular matrix (ECM) components. In oneembodiment, such ECM components can be derived from an animal lackingany functional expression of the alpha-1,3-GT gene. Extracelluar matrixmaterials can be derived from any tissue, including, but not limited to,skin, urinary, bladder or organ submucosal tissues. The scaffold canfunction as a prosthetic device. The scaffold can be synthesized fromfragmented ECM components, or in a preferred embodiment, is derived viadecellularization or processing of native tissue, thus removing livecells and leaving behind the ECM as a preformed scaffold with a 3-Dstructure and fiber configuration similar to the natural tissue. Thescaffold or device can be derived from matrix material obtained fromsoft tissue of an animal that lacks any functional expression ofalpha-1,3-Gal. The soft tissue can include, but is not limited to,dermis, organ submucosa (ie. small intestine submucosa (SIS)), thelateral meniscus removed from a knee joint, articlar cartilage removedfrom any joint, ligaments and/or tendons, such as the Achilles tendon.The tissue can then be processed as described below to obtain a matrixmaterial, such as biocompatible and bioresorbable fibers.

The extracellular matrix (ECM) is a complex structural entitysurrounding and supporting cells that are found within mammaliantissues. The ECM can also be referred to as connective tissue. The ECMis composed of structural proteins, such as collagen and elastin,specialized proteins, such as fibrillin, fibronectin, and laminin, andproteoglycans. Glycosaminoglycans (GAGs) are long chains of repeatingdisaccharide units forming extremely complex high molecular weightcomponents of the ECM. These disaccharide units contain an N-acetylatedhexosamine and provide lubrication and cross-links. Examples of GAGsinclude, but are not limited to, chondroitin 4-sulfate, chondroitin6-sulfate, keratan sulfate, dermatan sulfate, heparan sulfate andhyaluronic acid.

TABLE 1 Representative matrix types produced by vertebrate cells Colla-Cell-Surface gen Anchor Proteoglycan Receptor Cells I fibronectinchondroitin and Integrin fibroblasts dermatan sulfates II fibronectinchondroitin Integrin chondrocytes sulfate III fibronectin heparansulfate Integrin quiescent and heparin hepatocytes, epithelial; assoc.fibroblasts IV laminin heparan sulfate laminin all epithelial cells, andheparin receptors endothelial cells, regenerating hepatocytes Vfibronectin heparan sulfate Integrin quiescent and heparin fibroblastsVI fibronectin heparan sulfate Iitegrin quiescent fibroblasts

Collagens are the most abundant proteins found in the animal kingdom. Itis the major protein comprising the ECM. There are at least 12 types ofcollagen. Types I, II and III are the most abundant and form fibrils ofsimilar structure. Type IV collagen forms a two-dimensional reticulumand is a major component of the basal lamina. Collagens arepredominantly synthesized by fibroblasts but epithelial cells alsosynthesize these proteins. The fundamental higher order structure ofcollagens is a long and thin diameter rod-like protein. Type I collagenfor instance is approximately 300 nm long, 1.5 nm in diameter andconsists of 3 coiled subunits composed of two α1(I) chains and one α2(I)chain. Each chain consists of 1050 amino acids wound around each otherin a characteristic right-handed triple helix. There are 3 amino acidsper turn of the helix and every third amino acid is a Guanine. Collagensare also rich in proline and hydroxyproline. The bulky pyrollidone ringsof proline reside on the outside of the triple helix. Lateralinteractions of triple helices of collagens result in the formation offibrils roughly 50 nm diameter. The packing of collagen is such thatadjacent molecules are displaced approximately ¼ of their length (67nm). This staggered array produces a striated effect that can be seen inthe electron microscope.

Collagens are synthesized as longer precursor proteins calledprocollagens. Type I procollagen contains an additional 150 amino acidsat the N-terminus and 250 at the C-terminus. These pro-domains areglobular and form multiple intrachain disulfide bonds. The disulfidesstabilize the proprotein allowing the triple helical section to form.Collagen fibers begin to assemble in the endoplasmic reticulum (ER) andGolgi complexes. The signal sequence is removed and numerousmodifications take place in the collagen chains. Specific prolineresidues can be hydroxylated by prolyl 4-hydroxylase and prolyl3-hydroxylase. Specific lysine residues also are hydroxylated by lysylhydroxylase. Prolyl hydraoxylases are dependent upon vitamin C asco-factor. Glycosylations of the O-linked type also occurs during Golgitransit. Following completion of processing the procollagens aresecreted into the extracellular space where extracellular enzymes removethe pro-domains. The collagen molecules then polymerize to form collagenfibrils. Accompanying fibril formation is the oxidation of certainlysine residues by the extracellular enzyme lysyl oxidase fomingreactive aldehydes. These reactive aldehydes form specific cross-linksbetween two chains thereby, stabilizing the staggered array of thecollagens in the fibril.

TABLE 2 Types of Collagen Types Chain Composition Structural DetailsLocalization I [a1(I)]₂[α(I)] 300 nm, 67 nm banded skin, tendon, bone,fibrils etc. II [α1(II)]₃ 300 nm, small 67 nm cartilage, vitreousfibrils humor III [α1(III)]₃ 300 nm, small 67 nm skin, muscle, fibrilsfrequently with type I IV [α1(IV)₂[α2(IV)] 390 nm C-term globular allbasal lamina domain, nonfibrillar V [α1(V)][α2(V)][α3(V)] 390 nm N-termglobular most interstitial tissue, domain, small fibers assoc. with typeI VI [α1(VI)][α2(VI)][α3(VI)] 150 nm, N + C term. most interstitialtissue, globular domains, assoc. with type I microfibrils, 100 nm bandedfibrils VII [α1(VII)]₃ 450 nm, dimer epithelia VIII [α1(VIII)]₃ — someendothelial cells IX [α1(IX)][α2(IX)][α3(IX)] 200 nm, N-term. globularcartilage, assoc. with domain, bound type II proteoglycan X [α1(X)]₃ 150nm, C-term. globular hypertrophic and domain mineralizing cartilage XI[α1(XI)][α2(XI)][α3(XI)] 300 nm, small fibers cartilage XII α1(XII) —interacts with types I and III

The role of fibronectins is to attach cells to a variety ofextracellular matrices. Fibronectin attaches cells to all matricesexcept type IV that involves laminin as the adhesive molecule.Fibronectins are dimers of 2 similar peptides. Each chain isapproximately 60-70 nm long and 2-3 nm thick. At least 20 differentfibronectin chains have been identified that arise by alternative RNAsplicing of the primary transcript from a single fibronectin gene.Fibronectins contain at least 6 tightly folded domains each with a highaffinity for a different substrate such as heparan sulfate, collagen(separate domains for types I, II and III), fibrin and cell-surfacereceptors. The cell-surface receptor-binding domain contains a consensusamino acid sequence, RGDS.

All basal laminae contain a common set of proteins and GAGs. These aretype IV collagen, heparan sulfate proteoglycans, entactin and laminin.The basal lamina is often referred to as the type IV matrix. Each of thecomponents of the basal lamina is synthesized by the cells that restupon it. Laminin anchors cell surfaces to the basal lamina.

In one embodiment, any of the ECM components or combinations thereofdescribed above can be used to form a scaffold, which can optionally beused as a prosthetic device. The ECM-derived scaffold can alternativelybe produced by mechanical, chemical or enzymatic treatment of tissuefrom alpha 1,3 gal knockout pigs, such that all cells and debris areremoved leaving behind the ECM in a fiber pattern well suited forrecruitment of host cells and tissue regeneration. The scaffold orprosthetic device fabricated from biocompatible and bioresorbable fiberscan be surgically implanted into a region disposed between andconnecting two of the subject's bones, so as to provide normal motionand strength (for surgical implantation, see, for example, U.S. Pat.Nos. 6,042,610, 5,735,903, 5,479,033, 5,624,463, 5,306,311, 5,108,438,5,007,934 and 4,880,429). The prosthetic device can act as a scaffoldfor regenerating tissue since the physical characteristics of thescaffold encourage the in-growth of the new tissue. This can result in acomposite of the subject host body region and the prosthetic device thathas an in vivo outer surface contour that is substantially the same as anatural body region.

The device can be implanted into a region between and/or connecting twoof the subject's bones, the composite formed by the subject's bodyregion and the device can have an in vivo outer surface contoursubstantially the same as a natural region that is being treated. Thedevice can establish a biocompatible and partially bioresorbablescaffold adapted for ingrowth of fibrochondrocytes, fibroblasts orchondrocytes (such as meniscal fibrochondrocytes, vertebralfibrochondrocytes, etc.). The scaffold, together with the ingrown cellscan support natural load forces in the region.

In another embodiment, methods for fabricating a prosthetic devicehaving in vivo the shape desired (such as a segmental defect in ameniscus, for example) is provided. The method involves obtaining afiber matrix material from tissues of an animal lacking any functionalexpression of alpha-1,3-gal and placing this biocompatible and partiallybioresorbable fiber matrix into a mold defining the desired shape (Themold defines the outer surface of the device to complement the desiredbody region). The fibers can then be lyophilized and/or contacted with achemical cross-linking agent such that the fibers assume the shape ofthe mold. Alternatively, after the molding is completed, the structureor matrix formed in the mold can be cut so that its outer surface iscomplementary to a segmental defect. This method can yield a matrixadapted to have an outer surface contour complementary to that of thesegmental defect in the meniscus. This type of matrix can be implantedto correct a segmental defect of meniscus or as a meniscal augmentationdevice, the matrix can establish a biocompatible and an at leastpartially bioresorbable scaffold for ingrowth of meniscalfibrochondrocytes and for supporting natural meniscal load forces.

4. Hard and Soft Tissue Grafts

In another aspect of the invention, bone tendon bone grafts are providedthat can be useful in orthopedic surgery. Bone tendon bone grafts cancontain one or more bone blocks, and a tendon attached to the boneblocks. The bone blocks can be cut to provide a groove sufficient toaccommodate a fixation screw. Alternatively, a bone tendon bone graft isprovided that contains one or more bone blocks, wherein the bone blockis pre-shaped into a dowel, and a tendon attached to the bone blocks. Amethod to obtain bone tendon bone grafts is also provided whereby afirst bone plug having attached thereto a tendon or ligament is firstexcised and then a second bone plug having attached thereto a tendon orligament is excised; such that the first bone plug and the second boneplug are derived from contiguous bone stock and overlap such thatexcision of the first bone plug or the second bone plug forms a groovein the bone plug that is excised subsequent to the other.

In other embodiments, bone tendon bone grafts are provided that containa tendon and one bone block. The tendon can be looped around a bone tocreate a tendon, bone, tendon layer that can be held in place withsutures. This can also contain two trailing portions of the tendonavailable for fixation to secure the transplant. This type of graft canincrease tissue strength while decreasing shear that may cause tissuefailure by taking advantage of the natural cyclic creep associated withtendon movement to balance opposing forces in a pulley type fashion.

5. Skin Repair

In a further aspect of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in skin repair.

The skin can be divided into three layers: the epidermis, the dermis andthe subcutaneous layer. The epidermis is divided into four layers,starting from bottom to top: the basal cell layer, stratum spinosum,stratum granulosum, and stratum corneum.

The basal cell layer of the epidermis contains basal cells which divideand differentiate into other cells in the epidermis, and melanocytes,the cells that make melanin which gives skin its color. The stratumspinosum lies above the basal cell layer and is made of keratinocytes,cells that make the protein keratin. Keratin is an important componentof the stratum corneum as well as hair and nails. Cells in the stratumgranulosum are flattened and contain dark granules that are expelled andprovide the “cement” that holds cells together in the overlying stratumcorneum. This uppermost layer of the epidermis is actually made oftightly-packed layers of dead cells filled with keratin that form themajor physical barrier for the skin. The stratum corneum is thicker inareas like the palms and soles that withstand more daily wear and tearthan other parts of the body. The epidermis also contains Langerhanscells, which act as part of the skin's defense against infection. Thedermal-epidermal junction is where the epidermis meets the dermis. Thebasement membrane zone serves as the “glue” between these two layers.

The dermis is divided into the upper papillary dermis and the lowerreticular dermis. The structural components of the dermis includecollagen, elastic fibers, and ground substance. Nerves and blood vesselsalso course through the dermis. Skin appendages are the eccrine andapocrine sweat glands, hair follicles, sebaceous glands, and nails.Except for nails, all the skin appendages are located in the dermis.

The release of sweat from eccrine glands is the body's cooling process.Sweat is produced in a coiled tubule in the dermis and is transported bya sweat duct through the epidermis to be secreted. The entire bodysurface has about 2-3 million eccrine sweat glands and can produce up to10 L of sweat per day.

In humans, apocrine sweat glands serve no known function and areregarded as vestigial glands perhaps useful to our ancestors. They arelocated mainly in the underarm and genital areas. Like eccrine sweat,apocrine sweat is also produced in coiled tubules in the dermis, but theapocrine duct drains sweat into a hair follicle from which it reachesthe skins surface.

Hair is made of keratin, the same substance that forms nails and the toplayer of the epidermis (stratum corneum). Different cells located in theroot of the hair make keratin and melanin, which gives hair its color.Humans have two types of hair: vellus (light and fine) and terminal(dark and thick). A sebaceous gland secretes an oily substance calledsebum that drains into the canal of a hair follicle to reach the surfaceof the skin. Together, a hair follicle and its associated sebaceousgland are called a pilosebaceous unit. Hair follicles are distributedeverywhere on the body except the palms and soles. In humans, hair islargely decorative, but it also serves a protective function. Eyebrowsand eyelashes protect the eyes from dust and sun, while nasal hairsblock out foreign bodies from your nose. Scalp hair provides sometemperature insulation.

Sebaceous glands produce an oily substance called sebum. They are mostprominent in the skin of the scalp, face, and upper trunk and are absentfrom the palms and soles. As part of the pilosebaceous unit, sebaceousglands secrete sebum that drains into the follicular canal andeventually onto the surface of the skin. Sebaceous glands increase insize and produce more sebum in response to increased hormone levels,specifically androgen, during adolescence. They play an important rolein the development of acne.

The subcutaneous layer lies between the dermis and the underlying fasciacovering muscle. This layer is made of groups of adipocytes (fat cells)that are separated by fibrous septa. It serves three main functions: toinsulate the body from cold, to absorb trauma and cushion deepertissues, and to act as storage for the body's reserve fuel.

Nails are the only skin appendages that are not located in the dermisbut instead are located at the ends of fingers and toes. The nail plateis made of dead keratin, which forms a hard protective structure about0.3-0.65 mm thick. Keratin is formed in the nail matrix by dividingepidermal cells. The nail bed is the epithelial layer that is tightlyattached to the bottom of the nail plate. The blood vessels of the nailbed give nails their pink color. The proximal nail fold, or cuticle,protects the base of the nail from infection-causing organisms.

Nails grow at an average rate of 0.1 mm per day, and toenails growslower than fingernails. In a further embodiment, the hard and softtissue from animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in skin repair. Anycomponent or combination of skin components derived from such animalscan be used, including, but not limited to, the epidermal tissue, basalcell layer, stratum spinosum, stratum granulosum, stratum corneum,dermal tissue, upper papillary dermal tissue, lower reticular dermaltissue, collagen, elastic fibers, ground substance, eccrine glands,apocrine glands, hair follicles, sebaceous glands, nails, hair andsubcutaneous tissue. Such tissue can be used to replace human skin, forexample, to repair deep tissue burns of the skin.

Skin tissues include, but are not limited to, dermal or epidermal tissueor derivatives thereof. Below the skin is the fatty subcutaneous tissue.In one embodiment, the skin xenograft can include the epidermis. Inanother embodiment, the skin xenograft can include the epidermis and thedermis. The dermis can be provided in variable thicknesses, for example,1, 5, 10 or 20 mm. In addition, skin grafts are provided that containepidermis, dermis and subcutaneous tissue. In one embodiment skin graftthat contain epidermis, dermis and subcutaneous tissue can be used toreplace skin overlying bony areas or over tendons.

In another embodiment, skin tissue is used in its native form, or in ade-cellularized form, as a scaffold for repair or replacement of rotatorcuff, intrabdominal wall repair, gynecological or urological tissuerepair, as part of a process to repair or replace ligaments or tendons,or other soft tissue applications (for example as described in Table 6).The skin tissue xenograft can be a permanent replacement or used as atemporary replacement until the patient can regrow new skin. In oneembodiment, the skin graft can be used as a temporary substitute,Temporary skin substitutes can heal partial-thickness burns, promotewound healing and prevent infection, and can be used if a patient in nothealthy enough for reconstructive surgery. In another embodiment,permanent skin grafts are provided.

In further embodiments, different types of skin xenografts are provided.In one embodiment, the graft is a split-thickness grafts.Split-thickness grafts can contain the dermis with only a portion of theepidermis and can be used over burns or large wounds. In anotherembodiment, the graft is a full-thickness grafts. Full thickness graftscan include the epidermis and the dermis and can be used to cover smallareas. In a further embodiment, the graft can be a pedicle flaps orgrafts. Pedicle flaps or grafts can include the epidermis, the dermisand subcutaneous tissue. Pedicle flaps or grafts can be used to coverwounds or other areas that can require additional operations to repairbone, tendon, or nerve damage.

6. Internal Tissue Repair

In another aspect of the present invention, the hard and soft tissuefrom animals lacking any expression of functionalalpha-1,3-galactosyltransferase can be used in internal tissue repair,such as hernia repair, tendon pulleys, gliding surfaces, blood vesselanastamoses, heart valve repair or replacement and dura repair. Internaltissues include pericardial tissue, heart valves and submucosal tissue.In one embodiment, the submucosal tissue can be used to repair orreplace connective tissue.

In another embodiment, the xenograft tissue is prepared from adelaminated segment derived from submucosa of animal organs, preferablythe organ submucosa from an alpha 1,3 GT knockout pig. In a preferredembodiment the submucosa is derived from the intestinal tissue of ananimal. The segment can include the tunica submucosa and basilar tissueof the tunica mucosa, generally including the muscularis mucosa and thestratum compactum. The tunica submucosa and basilar mucosa tissue can bedelaminated from the tunica muscularis and the luminal portion of thetunica mucosa of the segment of intestinal tissue. This processing canresult in a tri-layer intestinal tissue segment that is tubular, verytough, fibrous, collagenous material (see, for example, U.S. Pat. Nos.4,902,508 and 4,956,178). In another embodiment, this tissue isextracted from mature animals, such as sows that, for example weighbetween 400 and 600 lbs. The tri-layer intestinal segments can be usedto form xenografts or they can be cut longitudinally or laterally toform elongated tissue segments. In either form, such segments have anintermediate portion and opposite end positions and opposite lateralportions which can be formed for surgical attachment to existingphysiological structures, using surgically acceptable techniques (seealso U.S. Pat. No. 5,372,821). In a related embodiment, the soft tissueis derived from dermal or skin tissue, which also can be formed or cutand used for surgical attachment to existing physiological structures.

In another embodiment, the invention provides a method for preparing orprocessing a soft tissue for engraftment into humans. An intact portionof tissue can be removed from any tissue of the animal. In oneembodiment, an intact heart can be removed from the animal and heartvalve tissues can then be excised, or pericardium can be harvested. Inother embodiments, tissues can include, but are not limited to,epithelium, connective tissue, blood, bone, cartilage, muscle, nerve,adenoid, adipose, areolar, bone, brown adipose, cancellous, muscle,cartaginous, cavernous, chondroid, chromaffin, dartoic, elastic,epithelial, fatty, fibrohyaline, fibrous, Gamgee, gelatinous,granulation, gut-associated lymphoid, Haller's vascular, hardhemopoietic, indifferent, interstitial, investing, islet, lymphatic,lymphoid, mesenchymal, mesonephric, mucous connective, multilocularadipose, myeloid, nasion soft, nephrogenic, nodal, osseous, osteogenic,osteoid, periapical, reticular, retiform, rubber, skeletal muscle,smooth muscle, and subcutaneous tissue.

In one embodiment, the tissue can be collected from freshly killedanimals. Alternatively, the tissue can be surgically removed from viableanimals. In one embodiment, after removal, the tissue can be placed in asuitable sterile isotonic or other tissue preserving solution.Harvesting of the tissue after slaughter of the animal can be done assoon as possible after slaughter and can be performed at coldtemperature. For example, between about 5° C. and about 20° C., about 0°C. and about 20° C., about 0° C. and about 10° C., or about 0° C. andabout 25° C. The harvested tissues and valves can be dissected free ofadjoining tissue. In one embodiment, a tissue or heart valve or portionthereof can be dissected free of adhering tissue, plaques,calcifications and the like. Alternatively, a tissue or valve can bedissected with portions of the surrounding tissue.

In one specific embodiment, tricuspid valves can be excised as separateleaflets. In another embodiment, tricuspid valves can be extracted as anintact valve including the fibrous ring surrounding theauriculo-ventricular orifice and the tendinous chords. In anotherembodiment, after dissection of the valve, the valve or valve portionscan be supported with stents, rings and the like. In another embodiment,peritoneum or pericardium can be harvested to form a heart valvexenografts or matrix material according to procedures known to those ofordinary skill in the art. (See, for example, U.S. Pat. No. 4,755,593 byLauren).

Soft tissue xenografts can be used in a variety of applications for therepair or reconstructions of human body parts, for example, thosedisclosed in Table 6.

Heart Valves

In one embodiment, heart valves are extracted from animals that lack anyexpression of alpha-1,3-Gal. Bovine, ovine, or porcine hearts, andspecifically porcine hearts, from animals lacking any functionalexpression of alpha-1,3-Gal, can serve as sources of heart valves. Heartvalves are composed of fibrochondrocytes and an extracellular matrix ofcollagen and elastic fibers, as well as a variety of proteoglycans.Types of heart valves include, but are not limited to the mitral valve,the atrial valve, the aortic valve, the tricuspid valve, pulmonaryvalve, plumonic patch, descending thoracic aorta, aortic non-valveconduit, pulmonic non-valve conduit with LPA and RPA, right or leftpulmonary hemi-artery with or without intact cusp, saphenous vein,aortoiliac, femoral vein, femoral artery and/or semi-lunar valve Incertain embodiments, tools can be used to secure a heart valveprosthesis to an aortic wall. Tools can include fasteners and/orreinforcements. In particular embodiments, heart valve prostheses canhave flexible leaflets. In one embodiment, the heart valve prosthesiscan be constructed from natural materials such as tissue, syntheticmaterials such as polymers or a combination thereof. In anotherembodiment, the valve prosthesis can be a tissue valve, and canadditionally include a stent, or be stentless, and be of porcine,bovine, or other animal tissue source. A heart valve xenograft preparedin accordance with the invention can have the general appearance of anative heart valve xenograft. The heart valve xenograft can also bevalve segments, such as individual leaflets, each of which may beimplanted into recipient heart. Alternatively, porcine pericardium canbe used to form the heart valve xenografts of the present invention.

The heart is a hollow, muscular organ that circulates blood throughoutan animal's body by contracting rhythmically. In mammals, the heart hasfour-chambers situated such that the right atrium and ventricle arecompletely separated from the left atrium and ventricle. Normally, bloodflows from systemic veins to the right atrium, and then to the rightventricle from which it is driven to the lungs via the pulmonary artery.Upon return from the lungs, the blood enters the left atrium, and thenflows to the left ventricle from which it is driven into the systematicarteries.

Four main heart valves prevent the backflow of blood during the rhythmiccontractions: the tricuspid, pulmonary, mitral, and aortic valves. Thetricuspid valve separates the right atrium and right ventricle, thepulmonary valve separates the right atrium and pulmonary artery, themitral valve separates the left atrium and left ventricle, and theaortic valve separates the left ventricle and aorta. Generally, patientshaving an abnormality of a heart valve are characterized as havingvalvular heart disease.

A heart valve can malfunction either by failing to open properly(stenosis) or by leaking (regurgitation). For example, a patient with amalfunctioning aortic valve can be diagnosed with either aortic valvestenosis or aortic valve regurgitation. In either case, valvereplacement by surgical means is a possible treatment. Replacementvalves can be autografts, allografts, or xenografts as well asmechanical valves or valves made partly from pig valves. Interestingly,cryopreserved allografts remain viable within the recipient patient formany years after transplantation. Unfortunately, replacement valves aresusceptible to problems such as degeneration, thrombosis, andcalcification.

The heart valve xenograft of the invention, or a segment thereof, can beimplanted into damaged human or animal hearts by those of skill in theart using known surgical techniques, for example, by open heart surgery,or minimally invasive techniques such as endoscopic surgery, andtransluminal implantation. Specific instruments for performing suchsurgical techniques are known to those of skill in the art, which ensureaccurate and reproducible placement of heart valve implants.

In a particular embodiment, heart valves as a prosthesis can be used forpatients with various forms of disease to the heart and/or valve.Porcine hearts can be obtained from market weight pigs (for example,pigs greater than 120 kg). After rinsing in sterile phosphate bufferedsaline, the hearts can be field dissected (apex removed) and shipped at4° C. in sterile PBS. All hearts can arrive at the processing center,for example, within 24 hr of animal slaughter. Aortic and pulmonaryvalves can be dissected as roots. In a specific embodiment, thesetissues can be subjected to a bioburden reduction step of incubation ina mixture of antibiotics and antimycotics for approximately 48 hr atapproximately 48° C. The disinfected tissues can either be cryopreserved(for example in 10% (v/v) DMSO and 10% (v/v) fetal bovine serum, −1°C./min) or can be decellularized by a procedure involving treatment withhypotonic medium followed by digestion with a mixture ofdeoxyribonuclease I and ribonuclease A. After 12 days, thedecellularized valves can either be cryopreserved or chemically fixed,for example, in 0.35% (w/v) glutaraldehyde at 2 mmHg in phosphatebuffered saline (pH 7.4) for a total of 7 days (the low pressurefixation ensures maintenance of the natural crimp of the collagenmatrix). In one embodiment, the fixed tissues is not cryopreserved, butcan be stored in a cross-fixing solution, such as a glutaraldehydesolution (such as 0.35% gluteraldehyde).

A tissue-based valve prosthesis can maintain structural elements, suchas leaflets, from its native form and/or structural elements can beincorporated into the prosthesis from the assembly of distinct pieces oftissue. For example, the valve prosthesis can be assembled from aporcine heart valve, from bovine pericardium or from a combinationthereof. Porcine tissue valves, for example, the Toronto SPV™ valvemarketed by St. Jude Medical, Inc. St. Paul, Minn., can be implanted inthe patient using the tools described herein. The Toronto SPV® valve isdesigned for implantation in an aortic heart valve position, see, forexample, David et al., J. Heart Valve Dis. 1:244-248 (1992). The toolsof the present invention are applicable to any valve, especially anytissue valve prosthesis, that is adapted for implanting in a patient.

Heart valve prosthesis includes a harvested tissue valve, such as acrosslinked porcine valve. Prosthesis can further include a sewingcover. The valve can have three leaflets, which can include a generallycylindrical base and three commissures support the leaflets.

In further embodiments, fasteners can be used to secure an heart valve,such as an aortic valve, prosthesis to the vessel wall. The fastenerscan be generally secured to the vessel wall during the implantationprocedure of the heart valve prosthesis. The fasteners can have a shapesimilar to a needle or nail, although the fastener can alternativelyhave a plurality of sharp tips. In addition, the fasteners can have oneor more barbs near the tips of the fasteners. The fastener can includean elongated portion with a tip end. The fastener can also have anoptional head at the end opposite tip end. In other embodiments, a barbcan be located at or near tip end. Fasteners can include two or morebarbs extending from the same or different sides of fastener. Thefasteners can be formed from a biocompatible material. Preferablebiocompatible materials for the fasteners yield the desired mechanicalproperties with respect to, for example, durability, mechanicalstrength, and flexibility/rigidity. Fasteners can be sufficiently rigidto hold their shape when pressure is applied by a physician to insertthe fastener. A fastener that is not sufficiently rigid may bend whenpressure is applied for insertion. Some bending may be tolerable as longas the fastener is able to penetrate the materials. A fastener withoutsufficient rigidity may not insert properly, thus increasing thepropensity of prosthesis damage, aortic wall damage, improper attachmentof the prosthesis and/or increased cross-clamp times. Afterimplantation, the fasteners can remain in the patient to secure thevalve prosthesis for the life-span of the prosthesis or at least untilthe healing process secures the valve to the vessel through cellulargrowth, if a bioresorbable material is used for the fastener. Thefasteners can be made from, for example, metal, ceramic, polymers orcombinations thereof. Suitable metals include, for example, titanium andstainless steel. Suitable ceramics include, for example, hydroxyapatite,such as bone fragments, carbon materials, such as graphite, and alumina.Suitable polymers include sufficiently rigid polymers, such aspolyetheretherketone (PEEK). The fasteners can also be formed frombioresorbable polymers, as described above, such that over time thefasteners are resorbed after sufficient tissue has been generated tosecure the valve prosthesis without the fasteners.

The length of the fastener can be between about 2 millimeters (mm) andabout 8 mm, for example, about 4 mm to about 7 mm. In one embodiment,the diameter of the elongated portion of the fastener can be less thanabout 2 mm, for example between about 0.2 mm and about 1.5 mm or betweenabout 0.2 mm and about 1 mm.

In other embodiments, methods of attaching a heart valve prosthesis to avessel wall can be based on the fasteners and the reinforcementsdescribed above. The reinforcements themselves can be secured eitherwith the fastener or other device. The fasteners can be deployed tosecure all of the elements simultaneously or one or more components canbe associated with each other or the valve prosthesis prior to the finaldeployment of the fasteners.

In one embodiment, the heart valves can be inserted into the heart, forexample, during an open heart procedure. In one embodiment, the processcan initiated by placing the subject, such as a human patient or primateor other large animal model, such as a sheep, on appropriate lifesupport and by opening the chest cavity to make the heart accessible.Then, a transverse aortotomy can be performed to make the natural valveaccessible through the vessel, such as the aorta. In one embodiment, thevessel is the aorta and the location for opening the aorta can depend onprecise structure of the prosthesis. For typical prosthesis, the aortagenerally can be cut about 1 cm from the sinotubular junction. Thedamaged or diseased natural valve is removed, preferably along with allcalcium and calcific debris. The aortic valve prosthesis can be placedbetween the aortic annulus, a slight narrowing where the aorta joins theheart, and the sinotubular junction, a slight narrowing of the aortajust down stream from the coronary arteries. However, the prosthesis canextend beyond the aortic annulus and/or the sinotubular junction. Forplacement at the aortic annulus, the prosthesis can be parachuted downthe severed aorta.

In additional embodiments, the heart valve prosthesis can be positionedat the site of implantation, adjacent to the appropriate vasculature,for example, the aorta. In one embodiment, the inflow edge of the valvecan be sutured or otherwise secured prior to securing the outflow edgewith the fasteners described herein, although the inflow edge can besecured after the outflow edge. In addition, it may be desirable to tackthe commissures in place prior to application of the fasteners describedherein. In a particular embodiment, the fasteners, the reinforcements,if any, and the prosthesis can be separate at the start of theimplantation procedure. Alternatively, the elements can bepre-assembled. In another embodiment, once the prosthesis is properlyaligned, a reinforcement can be placed in position and fasteners can besequentially inserted into an aperture in the reinforcement, through theprosthesis and through the aortic wall. When all the fasteners have beeninserted through one reinforcement, any additional reinforcements aresimilarly secured with fasteners. The fasteners can be inserted usingfinger pressure, forceps, a pusher tool, a hammer, or the like. Specificforceps can be used that specifically interface with the head of afastener. If there are no reinforcements, the fasteners are placed in adesired position and similarly inserted through the prosthesis andaortic wall.

In some embodiments, fasteners can be inserted into reinforcements priorto the initiation of the implantation procedure. The reinforcements canbe supplied to the surgeon with the fasteners inserted through or partlythrough apertures in the reinforcement. In these embodiments, the heador blunt end of the fasteners can stick out from the surface of thereinforcements. Thus, the procedure can be somewhat simplified relativeto a procedure in which all of the components are separate prior tobeginning the procedure. In these embodiments, once the prosthesis iscorrectly positioned in the vessel, a reinforcement with fasteners canbe aligned at a desired location, and the fasteners can be directlydeployed by pushing the fastener through the prosthesis and through thewall of the aorta. The fasteners can be inserted sequentially, and aplurality of reinforcements can be secured in this approach.

In alternative embodiments, one or more reinforcements can be attachedto the prosthesis prior to beginning the implantation procedure. Thereinforcements can be secured to the prosthesis by the manufacturer.Suture, biocompatible adhesive or other suitable fastener can be used tosecure a reinforcement to the prosthesis. Suitable biocompatibleadhesives include, for example, fibrin glue and other surgical glues.Once the prosthesis is correctly positioned, fasteners can besequentially or simultaneously placed within an aperture in thereinforcement and inserted through the prosthesis and the wall of theaorta. This can be continued until all of the fasteners are deployed.

In still other embodiments, the prostheses can be supplied withreinforcements in place and fasteners inserted in the reinforcements.The reinforcements can be secured to the prosthesis using the fastenerinserted through the reinforcement and, at least, partly through theprosthesis. Alternatively, the reinforcement can be secured to theprosthesis using suture, adhesive or other fastener. Once the prosthesisis in place within the animal or patient, each fastener can be pushedthrough the wall of the vessel to secure the prosthesis. In otherembodiments, conventional sutures, while effective and straightforward,can be used as fasteners.

7. Additional Applications for Xenografts

In a further aspect of the present invention, the tissue productsderived from animals lacking expression of functional alpha-1,3-GT canbe used to reconstruct body parts of a human. In certain embodiments,decellularized or cellularized dermal tissue, bone, ligaments, tendons,heart valves, nucleus pulposa, cartilage, meniscus, blood vessels,pericardium or other tissues described herein can be used, for example,as described in Table 6. In particular embodiments, the tissue can beused for human orthopedic reconstruction or repair, such as rotator cuffrepair, human skin repair, and/or human soft tissue repair. Thexenografts can be tested in a variety of animal models, such as primateor non-primate, such as sheep, models.

The xenografts can be applied using routine surgical procedures commonlyemployed for tissue graft applications. In one embodiment, for example,for use in non-vascular tissue graft applications, the tubular graftmaterial can be cut longitudinally and rolled out to form a “patch” oftissue. In another embodiment, tissue delamination can be carried out on“patches” of tissue, such as intestinal tissue, prepared by cutting theintestinal segment longitudinally and “unrolling” it to form a pre-graftpatch. The prepared graft tissue patches can be utilized, for example,as a skin graft material, for dura repair, or for repair of other bodytissue defects lending themselves to surgical application of a tissuegraft patch having the physical and functional characteristics of thepresent graft composition.

TABLE 6 Applications/Uses of Tissues harvested from Animals lacking anyexpression of functional alpha-1,3-GT Dermal Tissue, cellularized orde-cellularized Applications: Hernia Abdominal wall repair Rotator cuffrepair Slings to treat urinary incontinence Cosmetic surgery includingbreast reconstruction, facial defects, lip reconstruction, eyelid spacergrafts, depressed scar repair, Burns, skin replacement Mucosal graftsNasolabial folds Oral resurfacing Parotidectomy Rhinoplasty Septalperforation repair Temporary wound dressing Wound coverage TympanoplastyVestibuloplasty Other soft tissue defects Dermal tissue can be combinedwith the following additional materials: Growth factors to facilitatefaster healing, recruitment of cells (scaffold), in combination topromote hemostasis Anti-scarring (fibrinogen, Fibrin 1) BoneApplications: Use in fracture and small skeletal defect repair andosseous defects, gaps in bone, spinal repair, maxilliofacialreconstruction, dental implants Paste Bone plugs Bone implants ChipsScrews Rings (humeral, fibular, machined wedge) Dowels (unicortical,threaded cortical dowel,) Blocks (tricortical iliac block, unicorticalblock, bicortical block, cancellous block) Wedges (cortical wedge,patellar cortical wedge) Moldable strips Cancellous chips PowderVetebral fusions Femoral shafts Hemi femoral shafts Fibular shaftsHumeral shafts Tibial shafts Ilium strip tricordical Cancellous corticalstrips Cortical strips Intercalary grafts including femoral head with orwithout cartilage, whole or partial femur, proximal or distal femur,proximal or distal tibia Cortical cancellous chips Total jointreplacement Demineralized bone matrix Lordotic cortical block Bonetissue can be combined with any of the following additional materials:Growth factors (BMP) for non-union fracture repair Porcine gelatin as adelivery matrix Ligaments/Tendons Applications: ACL repair/replacementPCL repair/replacement Patellar tendon including bone Posterior tibialistendon Anterior tibialis tendon Semitendonosis tendon Gracilis tendonHeart Valves Applications/Types: Repair/replacement Aortic valvePulmonary valve Plumonic patch Descending thoracic aorta Aorticnon-valve conduit Pulmonic non-valve conduit with LPA and RPA Right/LeftPulmonary Hemi-artery with or without intact cusp Saphenous veinAortoiliac Femoral vein Femoral artery Heart valves can be combined withany of the following additional materials: Use of a ring material forsurgical insertion Nucleus Pulposa Applications: Inter-vertebralrepair/replacement Cartilage (cells) Applications: Cartilage replacement(replacement or as a scaffold to promote new cartilage growth).Cartilage can be combined with any of the following additionalmaterials: Growth factors to promote cellular infiltration MeniscusApplications: Repair/replacement Meniscus lateral with bone bridgeMeniscus medial with bone bridge Meniscus can be combined with any ofthe following additional materials: Plastic or metals to facilitateimplantation Blood Vessels Applications: Replacement/repair of bloodvessels, excluding those blood vessels associated with, or an integralpart of, whole organs for transplantation. Carotid arteryreplacement/repair Pericardium Applications: Patch used in surgicalprocedures when tissue regeneration is needed; works as a stabilizingand protective barrier at a surgical site Combination of othermaterials: Growth factors to facilitate faster healing, recruitment ofcells (scaffold), in combination to promote hemostasis Anti-scarring(fibrinogen, Fibrin 1) Small Intestine Submucosa Applications: rotatorcuff repair hernia abdominal wall repair slings to treat urinaryincontinence burns skin replacement cosmetic surgery including breastreconstruction, facial defects, lip reconstruction, eyelid spacergrafts, depressed scar repair, mucosal grafts, nasolavial folds, oralresurfacing, parotidectomy, septal perforation repair, rhinoplastytemporary wound dressing, wound coverage tympanoplasty vestibuloplastyother soft tissue defects vascular grafts, including venous, arterial orcapillary Other Soft Tissues HTO wedge to correct valgus and varusmisalignment Fascia used to correct uninary incontinenceII. Animals Lacking any Expression of FunctionalAlpha-1,3-Galactosyltransferase

Tissues from animals that lack any functional expression ofalpha-1,3-galactosyltransferase are provided. In one embodiment, theanimal is a porcine. In another embodiment, the animal is a bovine or anovine. In other embodiments, animals are provided in which one allele ofthe alpha-1,3-GT gene is inactivated via a genetic targeting event. Inanother aspect of the present invention, animals are provided in whichboth alleles of the alpha-1,3-GT gene are inactivated via a genetictargeting event. In one embodiment, the gene can be targeted viahomologous recombination. In other embodiments, the gene can bedisrupted, i.e. a portion of the genetic code can be altered, therebyaffecting transcription and/or translation of that segment of the gene.For example, disruption of a gene can occur through substitution,deletion (“knockout”) or insertion (“knockin”) techniques. Additionalgenes for a desired protein or regulatory sequence that modulatetranscription of an existing sequence can be inserted.

Animals besides old world monkeys and humans, such as pigs, that possesstwo inactive alleles of the alpha-1,3-GT gene are not naturallyoccurring. It was surprisingly discovered that while attempting toknockout the second allele of the alpha-1,3-GT gene through a genetictargeting event, a point mutation was identified, which rendered thesecond allele inactive.

Thus, in another aspect of the present invention, the alpha-1,3-GT genecan be rendered inactive through at least one point mutation. In oneembodiment, one allele of the alpha-1,3-GT gene can be rendered inactivethrough at least one point mutation. In another embodiment, both allelesof the alpha-1,3-GT gene can be rendered inactive through at least onepoint mutation. In one embodiment, this point mutation can occur via agenetic targeting event. In another embodiment, this point mutation canbe naturally occurring. In one specific embodiment the point mutationcan be a T-to-G mutation at the second base of exon 9 of thealpha-1,3-GT gene. Pigs carrying a naturally occurring point mutation inthe alpha-1,3-GT gene allow for the production of alpha1,3GT-deficientpigs free of antibiotic-resistance genes and thus have the potential tomake a safer product for human use. In other embodiments, at least two,at least three, at least four, at least five, at least ten or at leasttwenty point mutations can exist to render the alpha-1,3-GT geneinactive. In other embodiments, pigs are provided in which both allelesof the alpha-1,3-GT gene contain point mutations that prevent anyexpression of functional alpha1,3GT. In a specific embodiment, pigs areprovided that contain the T-to-G mutation at the second base of exon 9in both alleles of the alpha-1,3-GT gene.

Another aspect of the present invention provides an animal, in whichboth alleles of the alpha-1,3-GT gene are inactivated, whereby oneallele is inactivated by a genetic targeting event and the other alleleis inactivated via a naturally occurring point mutation. In oneembodiment, a porcine animal is provided, in which both alleles of thealpha-1,3-GT gene are inactivated, whereby one allele is inactivated bya genetic targeting event and the other allele is inactivated due topresence of a T-to-G point mutation at the second base of exon 9. In aspecific embodiment, a porcine animal is provided, in which both allelesof the alpha-1,3-GT gene are inactivated, whereby one allele isinactivated via a targeting construct directed to Exon 9 and the otherallele is inactivated due to presence of a T-to-G point mutation at thesecond base of exon 9.

Genetic Targeting of the Alpha-1,3-GT Gene

Animal cells that can be genetically modified can be obtained from avariety of different organs and tissues such as, but not limited to,skin, mesenchyme, lung, pancreas, heart, intestine, stomach, bladder,blood vessels, kidney, urethra, reproductive organs, and a disaggregatedpreparation of a whole or part of an embryo, fetus, or adult animal. Inone embodiment of the invention, cells can be selected from the groupconsisting of, but not limited to, epithelial cells, fibroblast cells,neural cells, keratinocytes, hematopoietic cells, melanocytes,chondrocytes, lymphocytes (B and T), macrophages, monocytes, mononuclearcells, cardiac muscle cells, other muscle cells, granulosa cells,cumulus cells, epidermal cells, endothelial cells, Islets of Langerhanscells, blood cells, blood precursor cells, bone cells, bone precursorcells, neuronal stem cells, primordial stem cells, hepatocytes,keratinocytes, umbilical vein endothelial cells, aortic endothelialcells, microvascular endothelial cells, fibroblasts, liver stellatecells, aortic smooth muscle cells, cardiac myocytes, neurons, Kupffercells, smooth muscle cells, Schwann cells, and epithelial cells,erythrocytes, platelets, neutrophils, lymphocytes, monocytes,eosinophils, basophils, adipocytes, chondrocytes, pancreatic isletcells, thyroid cells, parathyroid cells, parotid cells, tumor cells,glial cells, astrocytes, red blood cells, white blood cells,macrophages, epithelial cells, somatic cells, pituitary cells, adrenalcells, hair cells, bladder cells, kidney cells, retinal cells, rodcells, cone cells, heart cells, pacemaker cells, spleen cells, antigenpresenting cells, memory cells, T cells, B cells, plasma cells, musclecells, ovarian cells, uterine cells, prostate cells, vaginal epithelialcells, sperm cells, testicular cells, germ cells, egg cells, leydigcells, peritubular cells, sertoli cells, lutein cells, cervical cells,endometrial cells, mammary cells, follicle cells, mucous cells, ciliatedcells, nonkeratinized epithelial cells, keratinized epithelial cells,lung cells, goblet cells, columnar epithelial cells, squamous epithelialcells, osteocytes, osteoblasts, and osteoclasts.

In one alternative embodiment, embryonic stem cells can be used. Anembryonic stem cell line can be employed or embryonic stem cells can beobtained freshly from a host, such as a porcine animal. The cells can begrown on an appropriate fibroblast-feeder layer or grown in the presenceof leukemia inhibiting factor (LIF). In a preferred embodiment, thecells can be fibroblasts; in one specific embodiment, the cells can befetal fibroblasts. Fibroblast cells are a preferred somatic cell typebecause they can be obtained from developing fetuses and adult animalsin large quantities. These cells can be easily propagated in vitro witha rapid doubling time and can be clonally propagated for use in genetargeting procedures.

Targeting Constructs

Homologous Recombination

Homologous recombination permits site-specific modifications inendogenous genes and thus novel alterations can be engineered into thegenome. In homologous recombination, the incoming DNA interacts with andintegrates into a site in the genome that contains a substantiallyhomologous DNA sequence. In non-homologous (“random” or “illicit”)integration, the incoming DNA is not found at a homologous sequence inthe genome but integrates elsewhere, at one of a large number ofpotential locations. In general, studies with higher eukaryotic cellshave revealed that the frequency of homologous recombination is far lessthan the frequency of random integration. The ratio of these frequencieshas direct implications for “gene targeting” which depends onintegration via homologous recombination (i.e. recombination between theexogenous “targeting DNA” and the corresponding “target DNA” in thegenome).

A number of papers describe the use of homologous recombination inmammalian cells. Illustrative of these papers are Kucherlapati et al.,Proc. Natl. Acad. Sci. USA 81:3153-3157, 1984; Kucherlapati et al., Mol.Cell. Bio. 5:714-720, 1985; Smithies et al, Nature 317:230-234, 1985;Wake et al., Mol. Cell. Bio. 8:2080-2089, 1985; Ayares et al., Genetics111:375-388, 1985; Ayares et al., Mol. Cell. Bio. 7:1656-1662, 1986;Song et al., Proc. Natl. Acad. Sci. USA 84:6820-6824, 1987; Thomas etal. Cell 44:419-428, 1986; Thomas and Capecchi, Cell 51: 503-512, 1987;Nandi et al., Proc. Natl. Acad. Sci. USA 85:3845-3849, 1988; and Mansouret al., Nature 336:348-352, 1988. Evans and Kaufman, Nature 294:146-154,1981; Doetschman et al., Nature 330:576-578, 1987; Thoma and Capecchi,Cell 51:503-512, 4987; Thompson et al., Cell 56:316-321, 1989.

One aspect of the present invention uses homologous recombination toinactivate the alpha-1,3-GT gene in cells, such as the cells describedabove. The DNA can comprise at least a portion of the gene(s) at theparticular locus with introduction of an alteration into at least one,optionally both copies, of the native gene(s), so as to preventexpression of functional alpha1,3GT. The alteration can be an insertion,deletion, replacement or combination thereof. When the alteration isintroduce into only one copy of the gene being inactivated, the cellshaving a single unmutated copy of the target gene are amplified and canbe subjected to a second targeting step, where the alteration can be thesame or different from the first alteration, usually different, andwhere a deletion, or replacement is involved, can be overlapping atleast a portion of the alteration originally introduced. In this secondtargeting step, a targeting vector with the same arms of homology, butcontaining a different mammalian selectable markers can be used. Theresulting transformants are screened for the absence of a functionaltarget antigen and the DNA of the cell can be further screened to ensurethe absence of a wild-type target gene. Alternatively, homozygosity asto a phenotype can be achieved by breeding hosts heterozygous for themutation.

Targeting Vectors

Modification of a targeted locus of a cell can be produced byintroducing DNA into the cells, where the DNA has homology to the targetlocus and includes a marker gene, allowing for selection of cellscomprising the integrated construct. The homologous DNA in the targetvector will recombine with the chromosomal DNA at the target locus. Themarker gene can be flanked on both sides by homologous DNA sequences, a3′ recombination arm and a 5′ recombination arm. Methods for theconstruction of targeting vectors have been described in the art, see,for example, Dai et al., Nature Biotechnology 20: 251-255, 2002; WO00/51424.

Various constructs can be prepared for homologous recombination at atarget locus. The construct can include at least 50 bp, 100 bp, 500 bp,1 kbp, 2 kbp, 4 kbp, 5 kbp, 10 kbp, 15 kbp, 20 kbp, or 50 kbp ofsequence homologous with the target locus. The sequence can include anycontiguous sequence of the porcine alpha-1,3-GT gene (see, for example,GenBank Acc. No. L36152, WO0130992 to The University of Pittsburgh ofthe Commonwealth System of Higher Education; WO 01/123541 to Alexion,Inc.).

Various considerations can be involved in determining the extent ofhomology of target DNA sequences, such as, for example, the size of thetarget locus, availability of sequences, relative efficiency of doublecross-over events at the target locus and the similarity of the targetsequence with other sequences.

The targeting DNA can include a sequence in which DNA substantiallyisogenic flanks the desired sequence modifications with a correspondingtarget sequence in the genome to be modified. The substantially isogenicsequence can be at least about 95%, 97-98%, 99.0-99.5%, 99.6-99.9%, or100% identical to the corresponding target sequence (except for thedesired sequence modifications). The targeting DNA and the target DNApreferably can share stretches of DNA at least about 75, 150 or 500 basepairs that are 100% identical. Accordingly, targeting DNA can be derivedfrom cells closely related to the cell line being targeted; or thetargeting DNA can be derived from cells of the same cell line or animalas the cells being targeted.

The DNA constructs can be designed to modify the endogenous, targetalpha1,3GT. The homologous sequence for targeting the construct can haveone or more deletions, insertions, substitutions or combinationsthereof. The alteration can be the insertion of a selectable marker genefused in reading frame with the upstream sequence of the target gene.

Suitable selectable marker genes include, but are not limited to: genesconferring the ability to grow on certain media substrates, such as thetk gene (thymidine kinase) or the hprt gene (hypoxanthinephosphoribosyltransferase) which confer the ability to grow on HATmedium (hypoxanthine, aminopterin and thymidine); the bacterial gpt gene(guanine/xanthine phosphoribosyltransferase) which allows growth on MAXmedium (mycophenolic acid, adenine, and xanthine). See, for example,Song, K-Y., et al. Proc. Nat'l Acad. Sci. U.S.A. 84:6820-6824 (1987);Sambrook, J., et al., Molecular Cloning—A Laboratory Manual, Cold SpringHarbor Laboratory, Cold Spring Harbor, N.Y. (1989), Chapter 16. Otherexamples of selectable markers include: genes conferring resistance tocompounds such as antibiotics, genes conferring the ability to grow onselected substrates, genes encoding proteins that produce detectablesignals such as luminescence, such as green fluorescent protein,enhanced green fluorescent protein (eGFP). A wide variety of suchmarkers are known and available, including, for example, antibioticresistance genes such as the neomycin resistance gene (neo) (Southern,P., and P. Berg, J. Mol. Appl. Genet. 1:327-341 (1982)); and thehygromycin resistance gene (hyg) (Nucleic Acids Research 11:6895-6911(1983), and Te Riele, H., et al., Nature 348:649-651 (1990)). Otherselectable marker genes include: acetohydroxyacid synthase (AHAS),alkaline phosphatase (AP), beta galactosidase (LacZ), beta glucoronidase(GUS), chloramphenicol acetyltransferase (CAT), green fluorescentprotein (GFP), red fluorescent protein (RFP), yellow fluorescent protein(YFP), cyan fluorescent protein (CFP), horseradish peroxidase (HRP),luciferase (Luc), nopaline synthase (NOS), octopine synthase (OCS), andderivatives thereof. Multiple selectable markers are available thatconfer resistance to ampicillin, bleomycin, chloramphenicol, gentamycin,hygromycin, kanamycin, lincomycin, methotrexate, phosphinothricin,puromycin, and tetracycline.

Methods for the incorporation of antibiotic resistance genes andnegative selection factors will be familiar to those of ordinary skillin the art (see, e.g., WO 99/15650; U.S. Pat. No. 6,080,576; U.S. Pat.No. 6,136,566; Niwa et al., J. Biochem. 113:343-349 (1993); and Yoshidaet al., Transgenic Research 4:277-287 (1995)).

Combinations of selectable markers can also be used. For example, totarget alpha1,3GT, a neo gene (with or without its own promoter, asdiscussed above) can be cloned into a DNA sequence which is homologousto the alpha-1,3-GT gene. To use a combination of markers, the HSV-tkgene can be cloned such that it is outside of the targeting DNA (anotherselectable marker could be placed on the opposite flank, if desired).After introducing the DNA construct into the cells to be targeted, thecells can be selected on the appropriate antibiotics. In this particularexample, those cells which are resistant to G418 and gancyclovir aremost likely to have arisen by homologous recombination in which the neogene has been recombined into the alpha-1,3-GT gene but the tk gene hasbeen lost because it was located outside the region of the doublecrossover.

Deletions can be at least about 50 bp, more usually at least about 100bp, and generally not more than about 20 kbp, where the deletion cannormally include at least a portion of the coding region including aportion of or one or more exons, a portion of or one or more introns,and can or can not include a portion of the flanking non-coding regions,particularly the 5′-non-coding region (transcriptional regulatoryregion). Thus, the homologous region can extend beyond the coding regioninto the 5′-non-coding region or alternatively into the 3′-non-codingregion. Insertions can generally not exceed 10 kbp, usually not exceed 5kbp, generally being at least 50 bp, more usually at least 200 bp.

The region(s) of homology can include mutations, where mutations canfurther inactivate the target gene, in providing for a frame shift, orchanging a key amino acid, or the mutation can correct a dysfunctionalallele, etc. The mutation can be a subtle change, not exceeding about 5%of the homologous flanking sequences. Where mutation of a gene isdesired, the marker gene can be inserted into an intron or an exon.

The construct can be prepared in accordance with methods known in theart, various fragments can be brought together, introduced intoappropriate vectors, cloned, analyzed and then manipulated further untilthe desired construct has been achieved. Various modifications can bemade to the sequence, to allow for restriction analysis, excision,identification of probes, etc. Silent mutations can be introduced, asdesired. At various stages, restriction analysis, sequencing,amplification with the polymerase chain reaction, primer repair, invitro mutagenesis, etc. can be employed.

The construct can be prepared using a bacterial vector, including aprokaryotic replication system, e.g. an origin recognizable by E. coli,at each stage the construct can be cloned and analyzed. A marker, thesame as or different from the marker to be used for insertion, can beemployed, which can be removed prior to introduction into the targetcell. Once the vector containing the construct has been completed, itcan be further manipulated, such as by deletion of the bacterialsequences, linearization, introducing a short deletion in the homologoussequence. After final manipulation, the construct can be introduced intothe cell.

The present invention further includes recombinant constructs containingsequences of the alpha-1,3-GT gene. The constructs comprise a vector,such as a plasmid or viral vector, into which a sequence of theinvention has been inserted, in a forward or reverse orientation. Theconstruct can also include regulatory sequences, including, for example,a promoter, operably linked to the sequence. Large numbers of suitablevectors and promoters are known to those of skill in the art, and arecommercially available. The following vectors are provided by way ofexample. Bacterial: pBs, pQE-9 (Qiagen), phagescript, PsiX174,pBluescript SK, pBsKS, pNH8a, pNH16a, pNH18a, pNH46a (Stratagene);pTrc99A, pKK223-3, pKK233-3, pDR540, pRIT5 (Pharmacia). Eukaryotic:pWLneo, pSv2cat, pOG44, pXT1, pSG (Stratagene) pSVK3, pBPv, pMSG, pSVL(Pharmiacia), viral origin vectors (M13 vectors, bacterial phage 1vectors, adenovirus vectors, and retrovirus vectors), high, low andadjustable copy number vectors, vectors which have compatible repliconsfor use in combination in a single host (pACYC 184 and pBR322) andeukaryotic episomal replication vectors (pCDM8). Other vectors includeprokaryotic expression vectors such as pcDNA II, pSL301, pSE280, pSE380,pSE420, pTrcHisA, B, and C, pRSET A, B, and C (Invitrogen, Corp.),pGEMEX-1, and pGEMEX-2 (Promega, Inc.), the pET vectors (Novagen, Inc.),pTrc99A, pKK223-3, the pGEX vectors, pEZZ18, pRIT2T, and pMC1871(Pharmacia, Inc.), pKK233-2 and pKK388-1 (Clontech, Inc.), and pProEx-HT(Invitrogen, Corp.) and variants and derivatives thereof. Other vectorsinclude eukaryotic expression vectors such as pFastBac, pFastBacHT,pFastBacDUAL, pSFV, and pTet-Splice (Invitrogen), pEUK-C1, pPUR, pMAM,pMAMneo, pBI101, pBI121, pDR2, pCMVEBNA, and pYACneo (Clontech), pSVK3,pSVL, pMSG, pCH110, and pKK232-8 (Pharmacia, Inc.), p3′SS, pXT1, pSG5,pPbac, pMbac, pMClneo, and pOG44 (Stratagene, Inc.), and pYES2, pAC360,pBlueBacHis A, B, and C, pVL1392, pBlueBacIII, pCDM8, pcDNA1, pZeoSV,pcDNA3 pREP4, pCEP4, and pEBVHis (Invitrogen, Corp.) and variants orderivatives thereof. Additional vectors that can be used include: pUC18,pUC19, pBlueScript, pSPORT, cosmids, phagemids, YAC's (yeast artificialchromosomes), BAC's (bacterial artificial chromosomes), P1 (Escherichiacoli phage), pQE70, pQE60, pQE9 (quagan), pBS vectors, PhageScriptvectors, BlueScript vectors, pNH8A, pNH16A, pNH18A, pNH46A (Stratagene),pcDNA3 (Invitrogen), pGEX, pTrsfus, pTrc99A, pET-5, pET-9, pKK223-3,pKK233-3, pDR540, pRIT5 (Pharmacia), pSPORT1, pSPORT2, pCMVSPORT2.0 andpSV-SPORT1 (Invitrogen), pTrxFus, pThioHis, pLEX, pTrcHis, pTrcHis2,pRSET, pBlueBacHis2, pcDNA3.1/His, pcDNA3.1(−)/Myc-His, pSecTag,pEBVHis, pPIC9K, pPIC3.5K, pA0815, pPICZ, pPICZ, pGAPZ, pGAPZ,pBlueBac4.5, pBlueBacHis2, pMelBac, pSinRep5, pSinHis, pIND, pIND(SP1),pVgRXR, pcDNA2.1, pYES2, pZErO1.1, pZErO-2.1, pCR-Blunt, pSE280, pSE380,pSE420, pVL1392, pVL1393, pCDM8, pcDNA1.1, pcDNA1.1/Amp, pcDNA3.1,pcDNA3.1/Zeo, pSe, SV2, pRc/CMV2, pRc/RSV, pREP4, pREP7, pREP8, pREP9,pREP 10, pCEP4, pEBVHis, pCR3.1, pCR2.1, pCR3.1-Uni, and pCRBac fromInvitrogen; ExCell, gt11, pTrc99A, pKK223-3, pGEX-1 T, pGEX-2T,pGEX-2TK, pGEX-4T-1, pGEX-4T-2, pGEX-4T-3, pGEX-3X, pGEX-5X-1,pGEX-5X-2, pGEX-5X-3, pEZZ18, pRIT2T, pMC1871, pSVK3, pSVL, pMSG,pCH110, pKK232-8, pSL1180, pNEO, and pUC4K from Pharmacia;pSCREEN-1b(+), pT7Blue(R), pT7Blue-2, pCITE-4abc(+), pOCUS-2, pTAg,pET-32LIC, pET-30LIC, pBAC-2cp LIC, pBACgus-2cp LIC, pT7Blue-2 LIC,pT7Blue-2, SCREEN-1, BlueSTAR, pET-3abcd, pET-7abc, pET9abcd, pET11abcd,pET12abc, pET-14b, pET-15b, pET-16b, pET-17b-pET-17xb, pET-19b,pET-20b(+), pET-21abcd(+), pET-22b(+), pET-23abcd(+), pET-24abcd(+),pET-25b(+), pET-26b(+), pET-27b(+), pET-28abc(+), pET-29abc(+),pET-30abc(+), pET-31b(+), pET-32abc(+), pET-33b(+), pBAC-1, pBACgus-1,pBAC4x-1, pBACgus4x-1, pBAC-3cp, pBACgus-2cp, pBACsurf-1, plg, Signalplg, pYX, Selecta Vecta-Neo, Selecta Vecta-Hyg, and Selecta Vecta-Gptfrom Novagen; pLexA, pB42AD, pGBT9, pAS2-1, pGAD424, pACT2, pGAD GL,pGAD GH, pGAD10, pGilda, pEZM3, pEGFP, pEGFP-1, pEGFP-N, pEGFP-C, pEBFP,pGFPuv, pGFP, p6×His-GFP, pSEAP2-Basic, pSEAP2-Contral, pSEAP2-Promoter,pSEAP2-Enhancer, p gal-Basic, p gal-Control, p gal-Promoter, pgal-Enhancer, pCMV, pTet-Off, pTet-On, pTK-Hyg, pRetro-Off, pRetro-On,pIRESlneo, pIRES1hyg, pLXSN, pLNCX, pLAPSN, pMAMneo, pMAMneo-CAT,pMAMneo-LUC, pPUR, pSV2neo, pYEX4T-1/2/3, pYEX-S1, pBacPAK-His,pBacPAK8/9, pAcUW31, BacPAK6, pTriplEx, gt10, gt11, pWE15, and TriplExfrom Clontech; Lambda ZAP II, pBK-CMV, pBK-RSV, pBluescript II KS+/−,pBluescript II SK+/−, pAD-GAL4, pBD-GAL4 Cam, pSurfscript, Lambda FIXII, Lambda DASH, Lambda EMBL3, Lambda EMBL4, SuperCos, pCR-Scrigt Amp,pCR-Script Cam, pCR-Script Direct, pBS+/−, pBC KS+/−, pBC SK+/−,Phagescript, pCAL-n-EK, pCAL-n, pCAL-c, pCAL-kc, pET-3abcd, pET-11abcd,pSPUTK, pESP-1, pCMVLacI, pOPRSVI/MCS, pOPI3 CAT, pXT1, pSG5, pPbac,pMbac, pMClneo, pMClneo Poly A, pOG44, pOG45, pFRT GAL, pNEO GAL,pRS403, pRS404, pRS405, pRS406, pRS413, pRS414, pRS415, and pRS416 fromStratagene and variants or derivatives thereof. Two-hybrid and reversetwo-hybrid vectors can also be used, for example, pPC86, pDBLeu, pDBTrp,pPC97, p2.5, pGAD1-3, pGAD10, pACt, pACT2, pGADGL, pGADGH, pAS2-1,pGAD424, pGBT8, pGBT9, pGAD-GAL4, pLexA, pBD-GAL4, pHISi, pHISi-1,placZi, pB42AD, pDG202, pJK202, pJG4-5, pNLexA, pYESTrp and variants orderivatives thereof. Any other plasmids and vectors may be used as longas they are replicable and viable in the host.

Techniques which can be used to allow the DNA construct entry into thehost cell include calcium phosphate/DNA co precipitation, microinjectionof DNA into the nucleus, electroporation, bacterial protoplast fusionwith intact cells, transfection, or any other technique known by oneskilled in the art. The DNA can be single or double stranded, linear orcircular, relaxed or supercoiled DNA. For various techniques fortransfecting mammalian cells, see, for example, Keown et al., Methods inEnzymology Vol. 185, pp. 527-537 (1990).

In one specific embodiment, heterozygous knockout cells can be producedby transfection of primary fetal fibroblasts with a knockout vectorcontaining alpha-1,3-GT sequence isolated from isogenic DNA. Asdescribed in Dai et al. (Nature Biotechnology, 20:451-455), the 5′ armcan be 4.9 kb and be comprised of a large fragment of intron 8 and the5′ end of exon 9. The 3′ arm can be and be comprised of exon 9 sequence.The vector can incorporate a promoter trap strategy, using, for example,IRES (internal ribosome entry site) to initiate translation of the Neorgene.

Selection of Homologously Recombined Cells

The cells can then be grown in appropriately-selected medium to identifycells providing the appropriate integration. The presence of theselectable marker gene inserted into the alpha-1,3-GT gene establishesthe integration of the target construct into the host genome. Thosecells which show the desired phenotype can then be further analyzed byrestriction analysis, electrophoresis, Southern analysis, polymerasechain reaction, etc to analyze the DNA in order to establish whetherhomologous or non-homologous recombination occurred. This can bedetermined by employing probes for the insert and then sequencing the 5′and 3′ regions flanking the insert for the presence of the alpha-1,3-GTgene extending beyond the flanking regions of the construct oridentifying the presence of a deletion, when such deletion isintroduced. Primers can also be used which are complementary to asequence within the construct and complementary to a sequence outsidethe construct and at the target locus. In this way, one can only obtainDNA duplexes having both of the primers present in the complementarychains if homologous recombination has occurred. By demonstrating thepresence of the primer sequences or the expected size sequence, theoccurrence of homologous recombination is supported.

The polymerase chain reaction used for screening homologousrecombination events is known in the art, see, for example, Kim andSmithies, Nucleic Acids Res. 16:8887-8903, 1988; and Joyner et al.,Nature 338:153-156, 1989. The specific combination of a mutant polyomaenhancer and a thymidine kinase promoter to drive the neomycin gene hasbeen shown to be active in both embryonic stem cells and EC cells byThomas and Capecchi, supra, 1987; Nicholas and Berg (1983) inTeratocarcinoma Stem Cell, eds. Siver, Martin and Strikland (Cold SpringHarbor Lab., Cold Spring Harbor, N.Y. (pp. 469-497); and Linney andDonerly, Cell 35:693-699, 1983.

The cell lines obtained from the first round of targeting are likely tobe heterozygous for the targeted allele. Homozygosity, in which bothalleles are modified, can be achieved in a number of ways. One approachis to grow up a number of cells in which one copy has been modified andthen to subject these cells to another round of targeting using adifferent selectable marker. Alternatively, homozygotes can be obtainedby breeding animals heterozygous for the modified allele, according totraditional Mendelian genetics. In some situations, it can be desirableto have two different modified alleles. This can be achieved bysuccessive rounds of gene targeting or by breeding heterozygotes, eachof which carries one of the desired modified alleles.

Induced Mutation in the Alpha 1,3 GT Locus

In certain other embodiments, the methods of the invention involve theintentional introduction of a mutation via a mutagenic agent. Examplesof mutagenic agents known in the art and suitable for use in the presentinvention include, but are not limited to, chemical mutagens (e.g.,DNA-intercalating or DNA-binding chemicals such as N-ethyl-N-nitrosourea(ENU), ethylmethanesulphonate (EMS), mustard gas, ICR191 and the like;see, e.g., E. C. Friedberg, G. C. Walker, W. Siede, DNA Repair andMutagenesis, ASM Press, Washington D.C. (1995), physical mutagens (e.g.,UV radiation, radiation, x-rays), biochemical mutagens (e.g.,restriction enzymes, DNA repair mutagens, DNA repair inhibitors, anderror-prone DNA polymerases and replication proteins), as well astransposon insertion. According to the methods of the present invention,cells in culture can be exposed to one of these agents, and any mutationresulting in the depletion of galactose alpha1,3-galactose on the cellsurface can be selected, for example, via exposure to toxin A.

Preferred doses of chemical mutagens for inducing mutations in cells areknown in the art, or can be readily determined by the ordinarily skilledartisan using assays of mutagenesis known in the art. Chemicalmutagenesis of cells in vitro can be achieved by treating the cells withvarious doses of the mutagenic agent and/or controlling the time ofexposure to the agent. By titrating the mutagenic agent exposure and/ordose, it is possible to carry out the optimal degree of mutagenesis forthe intended purpose, thereby mutating a desired number of genes in eachtarget cell. For example, useful doses of ENU can be 0.1-0.4 mg/ml forapproximately 1-2 hours. In another example, useful doses of EMS can be0.1-1 mg/ml for approximately 10-30 hours. In addition, lower and higherdoses and exposure times can also be used to achieve the desiredmutation frequency.

Identification of Cells that do not Express Functional Alpha-1,3-GT

In one embodiment, the selection procedure can be based on a bacterialtoxin to select for cells that lack expression of functional alpha1,3GT. In another embodiment, the bacterial toxin, toxin A produced byClostridium difficile, can be used to select for cells lacking the cellsurface epitope galactose alpha1,3-galactose. Exposure to C. difficiletoxin can cause rounding of cells that exhibit this epitope on theirsurface, releasing the cells from the plate matrix. Both targeted geneknockouts and mutations that disable enzyme function or expression canbe detected using this selection method. Cells lacking cell surfaceexpression of the galactose alpha 1,3-galactose epitope, identifiedusing Toxin A mediated selection described, or produced using standardmethods of gene inactivation including gene targeting, can then be usedto produce animals, in which both alleles of the alpha 1,3 GT gene areinactive.

In one embodiment, the selection method can detect the depletion of thealpha 1,3GT epitope directly, whether due to targeted knockout of thealpha 1,3GT gene by homologous recombination, or a mutation in the genethat results in a nonfunctioning or nonexpressed enzyme. Selection viaantibiotic resistance has been used most commonly for screening (seeabove). This method can detect the presence of the resistance gene onthe targeting vector, but does not directly indicate whether integrationwas a targeted recombination event or a random integration. Certaintechnology, such as Poly A and promoter trap technology, increase theprobability of targeted events, but again, do not give direct evidencethat the desired phenotype, a cell deficient in gal alpha 1,3 galepitopes on the cell surface, has been achieved. In addition, negativeforms of selection can be used to select for targeted integration; inthese cases, the gene for a factor lethal to the cells is inserted insuch a way that only targeted events allow the cell to avoid death.Cells selected by these methods can then be assayed for gene disruption,vector integration and, finally, alpha 1,3gal epitope depletion. Inthese cases, since the selection is based on detection of targetingvector integration and not at the altered phenotype, only targetedknockouts, not point mutations, gene rearrangements or truncations orother such modifications can be detected.

In another embodiment, the selection procedure can be conducted usingserum containing complement factors and natural antibodies to the galalpha1,3gal epitope (see, for example, Koike et al., Xenotransplantation4:147-153, 1997). Exposure to serum from a human or non-human primatethat contains anti-Gal antibodies can cause cell lysis due to specificantibody binding and complement activation in cells that exhibit galalpha 1,3 gal epitope. Therefore, cells deficient in alpha-1,3-GT willremain alive and thus can be selected.

Animal cells believed to lacking expression of functional alpha-1,3-GTcan be further characterized. Such characterization can be accomplishedby the following techniques, including, but not limited to: PCRanalysis, Southern blot analysis, Northern blot analysis, specificlectin binding assays, and/or sequencing analysis.

PCR analysis as described in the art (see, for example, Dai et al.Nature Biotechnology 20:431-455) can be used to determine theintegration of targeting vectors. In one embodiment, amplimers canoriginate in the antibiotic resistance gene and extend into a regionoutside the vector sequence. Southern analysis (see, for example, Dai etal. Nature Biotechnology 20:431-455) can also be used to characterizegross modifications in the locus, such as the integration of a targetingvector into the alpha 1,3GT locus. Whereas, Northern analysis can beused to characterize the transcript produced from each of the alleles.

Specific lectin binding, using GSL IB4 lectin from Griffonia(Bandeiraea) simplicifolia (Vector Labs), a lectin that specificallybinds the carbohydrate moiety gal alpha 1,3 gal, and FACS (fluorescentantibody cell sorting) analysis of binding can determine whether or notthe alpha 1,3 gal epitope is present on the cells. This type of analysisinvolves the addition of fluorescein-labeled GSL-IB4 lectin to the cellsand subsequent cell sorting.

Further, sequencing analysis of the cDNA produced from the RNAtranscript can also be used to determine the precise location of anymutations in the alpha 1,3GT allele.

In yet another aspect, the present invention provides a method forproducing viable animals, such as pigs, in which both alleles of thealpha-1,3-GT gene have been rendered inactive. In one embodiment, theanimals are produced by cloning using a donor nucleus from a cell inwhich both alleles of the alpha-1,3-GT gene have been inactivated. Inone embodiment, both alleles of the alpha-1,3-GT gene are inactivatedvia a genetic targeting event. In another embodiment, both alleles ofthe alpha-1,3-GT gene are inactivated due to the presence of a pointmutation. In another embodiment, one allele is inactivated by a genetictargeting event and the other allele is inactivated via a pointmutation. In a further embodiment, one allele is inactivated by agenetic targeting event and the other allele is inactivated due topresence of a T-to-G point mutation at the second base of exon 9 of thealpha-1,3-GT gene. In a specific embodiment, one allele is inactivatedvia a targeting construct directed to Exon 9 and the other allele isinactivated due to presence of a T-to-G point mutation at the secondbase of exon 9 of the alpha-1,3-GT gene. In another embodiment, a methodto clone such animals, for example, pigs, includes: enucleating anoocyte, fusing the oocyte with a donor nucleus from a cell in which bothalleles of the alpha-1,3-GT gene have been inactivated, and implantingthe nuclear transfer-derived embryo into a surrogate mother.

Alternatively, a method is provided for producing viable animals thatlack any expression of functional alpha-1,3-GT by inactivating bothalleles of the alpha-1,3-GT gene in embryonic stem cells, which can thenbe used to produce offspring.

Genetically altered animals that can be created by modifying zygotesdirectly. For mammals, the modified zygotes can be then introduced intothe uterus of a pseudopregnant female capable of carrying the animal toterm. For example, if whole animals lacking the alpha-1,3-GT gene aredesired, then embryonic stem cells derived from that animal can betargeted and later introduced into blastocysts for growing the modifiedcells into chimeric animals. For embryonic stem cells, either anembryonic stem cell line or freshly obtained stem cells can be used.

In a suitable embodiment of the invention, the totipotent cells areembryonic stem (ES) cells. The isolation of ES cells from blastocysts,the establishing of ES cell lines and their subsequent cultivation arecarried out by conventional methods as described, for example, byDoetchmann et al., J. Embryol. Exp. Morph. 87:27-45 (1985); Li et al.,Cell 69:915-926 (1992); Robertson, E. J. “Tetracarcinomas and EmbryonicStem Cells: A Practical Approach,” ed. E. J. Robertson, IRL Press,Oxford, England (1987); Wurst and Joyner, “Gene Targeting: A PracticalApproach,” ed. A. L. Joyner, IRL Press, Oxford, England (1993); Hogen etal., “Manipulating the Mouse Embryo: A Laboratory Manual,” eds. Hogan,Beddington, Costantini and Lacy, Cold Spring Harbor Laboratory Press,New York (1994); and Wang et al., Nature 336:741-744 (1992). In anothersuitable embodiment of the invention, the totipotent cells are embryonicgerm (EG) cells. Embryonic Germ cells are undifferentiated cellsfunctionally equivalent to ES cells, that is they can be cultured andtransfected in vitro, then contribute to somatic and germ cell lineagesof a chimera (Stewart et al., Dev. Biol. 161:626-628 (1994)). EG cellsare derived by culture of primordial germ cells, the progenitors of thegametes, with a combination of growth factors: leukemia inhibitoryfactor, steel factor and basic fibroblast growth factor (Matsui et al.,Cell 70:841-847 (1992); Resnick et al., Nature 359:550-551 (1992)). Thecultivation of EG cells can be carried out using methods described inthe article by Donovan et al., “Transgenic Animals, Generation and Use,”Ed. L. M. Houdebine, Harwood Academic Publishers (1997), and in theoriginal literature cited therein.

Tetraploid blastocysts for use in the invention may be obtained bynatural zygote production and development, or by known methods byelectrofusion of two-cell embryos and subsequently cultured asdescribed, for example, by James et al., Genet. Res. Camb. 60:185-194(1992); Nagy and Rossant, “Gene Targeting: A Practical Approach,” ed. A.L. Joyner, IRL Press, Oxford, England (1993); or by Kubiak andTarkowski, Exp. Cell Res. 157:561-566 (1985).

The introduction of the ES cells or EG cells into the blastocysts can becarried out by any method known in the art. A suitable method for thepurposes of the present invention is the microinjection method asdescribed by Wang et al., EMBO J. 10:2437-2450 (1991).

Alternatively, by modified embryonic stem cells transgenic animals canbe produced. The genetically modified embryonic stem cells can beinjected into a blastocyst and then brought to term in a female hostmammal in accordance with conventional techniques. Heterozygous progenycan then be screened for the presence of the alteration at the site ofthe target locus, using techniques such as PCR or Southern blotting.After mating with a wild-type host of the same species, the resultingchimeric progeny can then be cross-mated to achieve homozygous hosts.

After transforming embryonic stem cells with the targeting vector toalter the alpha-1,3-GT gene, the cells can be plated onto a feeder layerin an appropriate medium, e.g., fetal bovine serum enhanced DMEM. Cellscontaining the construct can be detected by employing a selectivemedium, and after sufficient time for colonies to grow, colonies can bepicked and analyzed for the occurrence of homologous recombination.Polymerase chain reaction can be used, with primers within and withoutthe construct sequence but at the target locus. Those colonies whichshow homologous recombination can then be used for embryo manipulatingand blastocyst injection. Blastocysts can be obtained from superovulatedfemales. The embryonic stem cells can then be trypsinized and themodified cells added to a droplet containing the blastocysts. At leastone of the modified embryonic stem cells can be injected into theblastocoel of the blastocyst. After injection, at least one of theblastocysts can be returned to each uterine horn of pseudopregnantfemales. Females are then allowed to go to term and the resultinglitters screened for mutant cells having the construct. The blastocystsare selected for different parentage from the transformed ES cells. Byproviding for a different phenotype of the blastocyst and the ES cells,chimeric progeny can be readily detected, and then genotyping can beconducted to probe for the presence of the modified alpha-1,3-GT gene.

Somatic Cell Nuclear Transfer to Produce Cloned, Transgenic Offspring

The present invention provides a method for cloning an animal, such as apig, lacking a functional alpha-1,3-GT gene via somatic cell nucleartransfer. In general, the animal can be produced by a nuclear transferprocess comprising the following steps: obtaining desired differentiatedcells to be used as a source of donor nuclei; obtaining oocytes from theanimal; enucleating said oocytes; transferring the desireddifferentiated cell or cell nucleus into the enucleated oocyte, e.g., byfusion or injection, to form NT units; activating the resultant NT unit;and transferring said cultured NT unit to a host animal such that the NTunit develops into a fetus.

Nuclear transfer techniques or nuclear transplantation techniques areknown in the art (Dai et al. Nature Biotechnology 20:251-255; Polejaevaet al Nature 407:86-90 (2000); Campbell et al, Theriogenology, 43:181(1995); Collas et al, Mol. Report Dev., 38:264-267 (1994); Keefer et al,Biol. Reprod., 50:935-939 (1994); Sims et al, Proc. Natl. Acad. Sci.,USA, 90:6143-6147 (1993); WO 94/26884; WO 94/24274, and WO 90/03432,U.S. Pat. Nos. 4,944,384 and 5,057,420).

A donor cell nucleus, which has been modified to alter the alpha-1,3-GTgene, is transferred to a recipient oocyte. The use of this method isnot restricted to a particular donor cell type. The donor cell can be asdescribed herein, see also, for example, Wilmut et al Nature 385 810(1997); Campbell et al Nature 380 64-66 (1996); Dai et al., NatureBiotechnology 20:251-255, 2002 or Cibelli et al Science 280 1256-1258(1998). All cells of normal karyotype, including embryonic, fetal andadult somatic cells which can be used successfully in nuclear transfercan be employed. Fetal fibroblasts are a particularly useful class ofdonor cells. Generally suitable methods of nuclear transfer aredescribed in Campbell et al Theriogenology 43 181 (1995), Dai et al.Nature Biotechnology 20:251-255, Polejaeva et al Nature 407:86-90(2000), Collas et al Mol. Reprod. Dev. 38 264-267 (1994), Keefer et alBiol. Reprod. 50 935-939 (1994), Sims et al Proc. Nat'l. Acad. Sci. USA90 6143-6147 (1993), WO-A-9426884, WO-A-9424274, WO-A-9807841,WO-A-9003432, U.S. Pat. No. 4,994,384 and U.S. Pat. No. 5,057,420.Differentiated or at least partially differentiated donor cells can alsobe used. Donor cells can also be, but do not have to be, in culture andcan be quiescent. Nuclear donor cells which are quiescent are cellswhich can be induced to enter quiescence or exist in a quiescent statein vivo. Prior art methods have also used embryonic cell types incloning procedures (Campbell et al (Nature, 380:64-68, 1996) and Sticeet al (Biol. Reprod., 20 54:100-110, 1996).

Somatic nuclear donor cells may be obtained from a variety of differentorgans and tissues such as, but not limited to, skin, mesenchyme, lung,pancreas, heart, intestine, stomach, bladder, blood vessels, kidney,urethra, reproductive organs, and a disaggregated preparation of a wholeor part of an embryo, fetus, or adult animal. In a suitable embodimentof the invention, nuclear donor cells are selected from the groupconsisting of epithelial cells, fibroblast cells, neural cells,keratinocytes, hematopoietic cells, melanocytes, chondrocytes,lymphocytes (B and T), macrophages, monocytes, mononuclear cells,cardiac muscle cells, other muscle cells, granulosa cells, cumuluscells, epidermal cells or endothelial cells. In another embodiment, thenuclear donor cell is an embryonic stem cell. In a preferred embodiment,fibroblast cells can be used as donor cells.

In another embodiment of the invention, the nuclear donor cells of theinvention are germ cells of an animal. Any germ cell of an animalspecies in the embryonic, fetal, or adult stage may be used as a nucleardonor cell. In a suitable embodiment, the nuclear donor cell is anembryonic germ cell.

Nuclear donor cells may be arrested in any phase of the cell cycle (G0,G1, G2, S, M) so as to ensure coordination with the acceptor cell. Anymethod known in the art may be used to manipulate the cell cycle phase.Methods to control the cell cycle phase include, but are not limited to,G0 quiescence induced by contact inhibition of cultured cells, G0quiescence induced by removal of serum or other essential nutrient, G0quiescence induced by senescence, G0 quiescence induced by addition of aspecific growth factor; G0 or G1 quiescence induced by physical orchemical means such as heat shock, hyperbaric pressure or othertreatment with a chemical, hormone, growth factor or other substance;S-phase control via treatment with a chemical agent which interfereswith any point of the replication procedure; M-phase control viaselection using fluorescence activated cell sorting, mitotic shake off,treatment with microtubule disrupting agents or any chemical whichdisrupts progression in mitosis (see also Freshney, R. I., “Culture ofAnimal Cells: A Manual of Basic Technique,” Alan R. Liss, Inc, New York(1983).

Methods for isolation of oocytes are well known in the art. Essentially,this can comprise isolating oocytes from the ovaries or reproductivetract of an animal. A readily available source of oocytes isslaughterhouse materials. For the combination of techniques such asgenetic engineering, nuclear transfer and cloning, oocytes mustgenerally be matured in vitro before these cells can be used asrecipient cells for nuclear transfer, and before they can be fertilizedby the sperm cell to develop into an embryo. This process generallyrequires collecting immature (prophase I) oocytes from mammalianovaries, e.g., bovine ovaries obtained at a slaughterhouse, and maturingthe oocytes in a maturation medium prior to fertilization or enucleationuntil the oocyte attains the metaphase II stage, which in the case ofbovine oocytes generally occurs about 18-24 hours post-aspiration. Thisperiod of time is known as the “maturation period”. In certainembodiments, the oocyte is obtained from a gilt. A “gilt” is a femalepig that has never had offspring. In other embodiments, the oocyte isobtained from a sow. A “sow” is a female pig that has previouslyproduced offspring.

A metaphase II stage oocyte can be the recipient oocyte, at this stageit is believed that the oocyte can be or is sufficiently “activated” totreat the introduced nucleus as it does a fertilizing sperm. MetaphaseII stage oocytes, which have been matured in vivo have been successfullyused in nuclear transfer techniques. Essentially, mature metaphase IIoocytes can be collected surgically from either non-superovulated orsuperovulated animal 35 to 48, or 39-41, hours past the onset of estrusor past the injection of human chorionic gonadotropin (hCG) or similarhormone. The oocyte can be placed in an appropriate medium, such as ahyalurodase solution.

After a fixed time maturation period, which ranges from about 10 to 40hours, about 16-18 hours, about 40-42 hours or about 39-41 hours, theoocytes can be enucleated. Prior to enucleation the oocytes can beremoved and placed in appropriate medium, such as HECM containing 1milligram per milliliter of hyaluronidase prior to removal of cumuluscells. The stripped oocytes can then be screened for polar bodies, andthe selected metaphase II oocytes, as determined by the presence ofpolar bodies, are then used for nuclear transfer. Enucleation follows.

Enucleation can be performed by known methods, such as described in U.S.Pat. No. 4,994,384. For example, metaphase II oocytes can be placed ineither HECM, optionally containing 7.5 micrograms per millilitercytochalasin B, for immediate enucleation, or can be placed in asuitable medium, for example an embryo culture medium such as CR1aa,plus 10% estrus cow serum, and then enucleated later, preferably notmore than 24 hours later, and more preferably 16-18 hours later.

Enucleation can be accomplished microsurgically using a micropipette toremove the polar body and the adjacent cytoplasm. The oocytes can thenbe screened to identify those of which have been successfullyenucleated. One way to screen the oocytes is to stain the oocytes with 1microgram per milliliter 33342 Hoechst dye in HECM, and then view theoocytes under ultraviolet irradiation for less than 10 seconds. Theoocytes that have been successfully enucleated can then be placed in asuitable culture medium, for example, CR1aa plus 10% serum.

A single mammalian cell of the same species as the enucleated oocyte canthen be transferred into the perivitelline space of the enucleatedoocyte used to produce the NT unit. The mammalian cell and theenucleated oocyte can be used to produce NT units according to methodsknown in the art. For example, the cells can be fused by electrofusion.

Electrofusion is accomplished by providing a pulse of electricity thatis sufficient to cause a transient breakdown of the plasma membrane.This breakdown of the plasma membrane is very short because the membranereforms rapidly. Thus, if two adjacent membranes are induced tobreakdown and upon reformation the lipid bilayers intermingle, smallchannels can open between the two cells. Due to the thermodynamicinstability of such a small opening, it enlarges until the two cellsbecome one. See, for example, U.S. Pat. No. 4,997,384 by Prather et al.A variety of electrofusion media can be used including, for example,sucrose, mannitol, sorbitol and phosphate buffered solution. Fusion canalso be accomplished using Sendai virus as a fusogenic agent (Graham,Wister Inot. Symp. Monogr., 9, 19, 1969). Also, the nucleus can beinjected directly into the oocyte rather than using electroporationfusion. See, for example, Collas and Barnes, Mol. Reprod. Dev.,38:264-267 (1994). After fusion, the resultant fused NT units are thenplaced in a suitable medium until activation, for example, CR1 aamedium. Typically activation can be effected shortly thereafter, forexample less than 24 hours later, or about 4-9 hours later, or optimally1-2 hours after fusion. In a preferred embodiment, activation occurs atleast one hour post fusion and at 40-41 hours post maturation.

The NT unit can be activated by known methods. Such methods include, forexample, culturing the NT unit at sub-physiological temperature, inessence by applying a cold, or actually cool temperature shock to the NTunit. This can be most conveniently done by culturing the NT unit atroom temperature, which is cold relative to the physiologicaltemperature conditions to which embryos are normally exposed.Alternatively, activation can be achieved by application of knownactivation agents. For example, penetration of oocytes by sperm duringfertilization has been shown to activate prefusion oocytes to yieldgreater numbers of viable pregnancies and multiple genetically identicalcalves after nuclear transfer. Also, treatments such as electrical andchemical shock can be used to activate NT embryos after fusion. See, forexample, U.S. Pat. No. 5,496,720, to Susko-Parrish et al. Fusion andactivation can be induced by application of an AC pulse of 5 V for 5 sfollowed by two DC pulses of 1.5 kV/cm for 60 μs each using an ECM2001Electrocell Manipulator (BTX Inc., San Diego, Calif.). Additionally,activation can be effected by simultaneously or sequentially byincreasing levels of divalent cations in the oocyte, and reducingphosphorylation of cellular proteins in the oocyte. This can generallybe effected by introducing divalent cations into the oocyte cytoplasm,e.g., magnesium, strontium, barium or calcium, e.g., in the form of anionophore. Other methods of increasing divalent cation levels includethe use of electric shock, treatment with ethanol and treatment withcaged chelators. Phosphorylation can be reduced by known methods, forexample, by the addition of kinase inhibitors, e.g., serine-threoninekinase inhibitors, such as 6-dimethyl-aminopurine, staurosporine,2-aminopurine, and sphingosine. Alternatively, phosphorylation ofcellular proteins can be inhibited by introduction of a phosphatase intothe oocyte, e.g., phosphatase 2A and phosphatase 2B.

The activated NT units, or “fused embryos”, can then be cultured in asuitable in vitro culture medium until the generation of cell colonies.Culture media suitable for culturing and maturation of embryos are wellknown in the art. Examples of known media, which can be used for embryoculture and maintenance, include Ham's F-10+10% fetal calf serum (FCS),Tissue Culture Medium-199 (TCM-199)+10% fetal calf serum,Tyrodes-Albumin-Lactate-Pyruvate (TALP), Dulbecco's Phosphate BufferedSaline (PBS), Eagle's and Whitten's media, and, in one specific example,the activated NT units can be cultured in NCSU-23 medium for about 1-4 hat approximately 38.6° C. in a humidified atmosphere of 5% CO2.

Afterward, the cultured NT unit or units can be washed and then placedin a suitable media contained in well plates which preferably contain asuitable confluent feeder layer. Suitable feeder layers include, by wayof example, fibroblasts and epithelial cells. The NT units are culturedon the feeder layer until the NT units reach a size suitable fortransferring to a recipient female, or for obtaining cells which can beused to produce cell colonies. Preferably, these NT units can becultured until at least about 2 to 400 cells, about 4 to 128 cells, orat least about 50 cells.

Activated NT units can then be transferred (embryo transfers) to theoviduct of an female pigs. In one embodiment, the female pigs can be anestrus-synchronized recipient gilt. Crossbred gilts (largewhite/Duroc/Landrace) (280-400 lbs) can be used. The gilts can besynchronized as recipient animals by oral administration of 18-20 mgRegu-Mate (Altrenogest, Hoechst, Warren, N.J.) mixed into the feed.Regu-Mate can be fed for 14 consecutive days. One thousand units ofHuman Chorionic Gonadotropin (hCG, Intervet America, Millsboro, Del.)can then be administered i.m. about 105 h after the last Regu-Matetreatment. Embryo transfers can then be performed about 22-26 h afterthe hCG injection. In one embodiment, the pregnancy can be brought toterm and result in the birth of live offspring. In another embodiment,the pregnancy can be terminated early and embryonic cells can beharvested.

Breeding for Desired Homozygous Knockout Animals

In another aspect, the present invention provides a method for producingviable animals that lack any expression of functional alpha-1,3-GT isprovided by breeding a male heterozygous for the alpha-1,3-GT gene witha female heterozygous for the alpha-1,3-GT gene. In one embodiment, theanimals are heterozygous due to the genetic modification of one alleleof the alpha-1,3-GT gene to prevent expression of that allele. Inanother embodiment, the animals are heterozygous due to the presence ofa point mutation in one allele of the alpha-1,3-GT gene. In anotherembodiment, the point mutation can be a T-to-G point mutation at thesecond base of exon 9 of the alpha-1,3-GT gene. In one specificembodiment, a method to produce an animal that lacks any expression offunctional alpha-1,3-GT is provided wherein a male pig that contains aT-to-G point mutation at the second base of exon 9 of the alpha-1,3-GTgene is bred with a female pig that contains a T-to-G point mutation atthe second base of exon 9 of the alpha-1,3-GT gene.

In one embodiment, sexually mature animals produced from nucleartransfer from donor cells that carrying a double knockout in thealpha-1,3-GT gene, can be bred and their offspring tested for thehomozygous knockout. These homozygous knockout animals can then be bredto produce more animals.

In another embodiment, oocytes from a sexually mature double knockoutanimal can be in vitro fertilized using wild type sperm from twogenetically diverse pig lines and the embryos implanted into suitablesurrogates. Offspring from these matings can be tested for the presenceof the knockout, for example, they can be tested by cDNA sequencing,PCR, toxin A sensitivity and/or lectin binding. Then, at sexualmaturity, animals from each of these litters can be mated.

In certain methods according to this aspect of the invention,pregnancies can be terminated early so that fetal fibroblasts can beisolated and further characterized phenotypically and/or genotypically.Fibroblasts that lack expression of the alpha-1,3-GT gene can then beused for nuclear transfer according to the methods described herein (seealso Dai et al.) to produce multiple pregnancies and offspring carryingthe desired double knockout.

III. Types of Genetically Modified Animals/Additional GeneticModifications

In one aspect of the present invention, animals are provided in whichone allele of the alpha-1,3-GT gene is inactivated via a genetictargeting event. In another aspect of the present invention, porcineanimals are provided in which both alleles of the alpha-1,3-GT gene areinactivated via a genetic targeting event. In one embodiment, the genecan be targeted via homologous recombination. In other embodiments, thegene can be disrupted, i.e. a portion of the genetic code can bealtered, thereby affecting transcription and/or translation of thatsegment of the gene. For example, disruption of a gene can occur throughsubstitution, deletion (“knockout”) or insertion (“knockin”) techniques.Additional genes for a desired protein or regulatory sequence thatmodulate transcription of an existing sequence can be inserted.

Thus, in another aspect of the present invention, the alpha-1,3-GT genecan be rendered inactive through at least one point mutation. In oneembodiment, one allele of the alpha-1,3-GT gene can be rendered inactivethrough at least one point mutation. In another embodiment, both allelesof the alpha-1,3-GT gene can be rendered inactive through at least onepoint mutation. In one embodiment, this point mutation can occur via agenetic targeting event. In another embodiment, this point mutation canbe naturally occurring. In one specific embodiment the point mutationcan be a T-to-G mutation at the second base of exon 9 of thealpha-1,3-GT gene (FIG. 1). Pigs carrying a naturally occurring pointmutation in the alpha-1,3-GT gene allow for the production ofalpha1,3GT-deficient pigs free of antibiotic-resistance genes and thushave the potential to make a safer product for human use. In otherembodiments, at least two, at least three, at least four, at least five,at least ten or at least twenty point mutations can exist to render thealpha-1,3-GT gene inactive. In other embodiments, pigs are provided inwhich both alleles of the alpha-1,3-GT gene contain point mutations thatprevent any expression of functional alpha1,3GT. In a specificembodiment, pigs are provided that contain the T-to-G mutation at thesecond base of exon 9 in both alleles of the alpha-1,3-GT gene (FIG. 1).

Another aspect of the present invention provides an animal, in whichboth alleles of the alpha-1,3-GT gene are inactivated, whereby oneallele is inactivated by a genetic targeting event and the other alleleis inactivated via a naturally occurring point mutation. In oneembodiment, a porcine animal is provided, in which both alleles of thealpha-1,3-GT gene are inactivated, whereby one allele is inactivated bya genetic targeting event and the other allele is inactivated due topresence of a T-to-G point mutation at the second base of exon 9. In aspecific embodiment, a porcine animal is provided, in which both allelesof the alpha-1,3-GT gene are inactivated, whereby one allele isinactivated via a targeting construct directed to Exon 9 (FIG. 6) andthe other allele is inactivated due to presence of a T-to-G pointmutation at the second base of exon 9.

In a further embodiment, tissue can be obtained from animals lacking anyfunctional expression of the alpha-1,3-GT gene that also can containadditional genetic modifications. Such genetic modifications can includeadditions and/or deletions of other genes to prevent rejection, promotewound healing, and/or minimize or eliminate unwanted pathogens (such asprions or retroviruses).

PERV refers to a family of retrovirus of which three main classes havebeen identified to date: PERV-A (Genbank Accession No. AF038601), PERV-B(EMBL Accession No. PERY17013) and PERV-C (Genbank Accession No.AF038600) (Patience et al 1997, Akiyoshi et al 1998). The gag and polgenes of PERV-A, B, and C are highly homologous, it is the env gene thatdiffers between the different types of PERV (eg., PERV-A, PERV-B,PERV-C). PERV-D has also recently been identified (see, for example,U.S. Pat. No. 6,261,806).

In one of the present invention, porcine endogenous retrovirus (PERV)genes can be regulated by the expression interfering RNA molecules(iRNA). For example, at least two iRNA molecules can be used so that theexpression of the PERV virus is functionally eliminated or belowdetection levels (see, for example, U.S. Ser. No. 60/523,938). In afurther embodiment, other viruses, including but not limited to porcinerespiratory and reproductive syndrome (PRRS) virus are inactivated ordown modulated either via homologous recombination or using aninhibitory RNA (RNAi) approach. In the case of down regulation usingRNAi, gene sequences encoding small inhibitory RNAs are expressed as atransgene and introduced into pigs either via microinjection, ICSI,nuclear transfer, or using sperm mediated gene transfer.

In another embodiment, the expression of additional genes responsiblefor xenograft rejection can be eliminated or reduced. Such genesinclude, but are not limited to the CMP-NEUAc Hydroxylase Gene, theisoGloboside 3 Synthase gene, and the Forssman synthase gene. Inaddition, genes or cDNA encoding complement related proteins, which areresponsible for the suppression of complement mediated lysis can also beexpressed in the animals and tissues of the present invention. Suchgenes include, but are not limited to CD59, DAF, MCP and CD46 (see, forexample, WO 99/53042; Chen et al. Xenotransplantation, Volume 6 Issue 3Page 194—August 1999, which describes pigs that express CD59/DAFtransgenes; Costa C et al, Xenotransplantation. 2002 January;9(1):45-57, which describes transgenic pigs that express human CD59 andH-transferase; Zhao L et al.; Diamond L E et al. Transplantation. 2001Jan. 15; 71(1):132-42, which describes a human CD46 transgenic pigs.

Additional modifications can include expression of tissue factor pathwayinhibitor (TFPI). heparin, antithrombin, hirudin, TFPI, tickanticoagulant peptide, or a snake venom factor, such as described in WO98/42850 and U.S. Pat. No. 6,423,316, entitled “Anticoagulant fusionprotein anchored to cell membrane”; or compounds, such as antibodies,which down-regulate the expression of a cell adhesion molecule by thecells, such as described in WO 00/31126, entitled “Suppression ofxenograft rejection by down regulation of a cell adhesion molecules” andcompounds in which co-stimulation by signal 2 is prevented, such as byadministration to the organ recipient of a soluble form of CTLA-4 fromthe xenogeneic donor organism, for example as described in WO 99/57266,entitled “Immunosuppression by blocking T cell co-stimulation signal 2(B7/CD28 interaction)”.

Certain aspects of the invention are described in greater detail in thenon-limiting Examples that follow.

EXAMPLES Example 1 Production of Porcine Cells Heterozygous for theAlpha-1,3-GT Gene

Isolation and Transfection of Primary Porcine Fetal Fibroblasts.

Fetal fibroblast cells (PCFF4-1 to PCFF4-10) were isolated from 10fetuses of the same pregnancy at day 33 of gestation. After removing thehead and viscera, fetuses were washed with Hanks' balanced salt solution(HBSS; Gibco-BRL, Rockville, Md.), placed in 20 ml of HBSS, and dicedwith small surgical scissors. The tissue was pelleted and resuspended in50-ml tubes with 40 ml of DMEM and 100 U/ml collagenase (Gibco-BRL) perfetus. Tubes were incubated for 40 min in a shaking water bath at 37° C.The digested tissue was allowed to settle for 3-4 min and the cell-richsupernatant was transferred to a new 50-ml tube and pelleted. The cellswere then resuspended in 40 ml of DMEM containing 10% fetal calf serum(FCS), 1× nonessential amino acids, 1 mM sodium pyruvate and 2 ng/mlbFGF, and seeded into 10 cm. dishes. All cells were cryopreserved uponreaching confluence. SLA-1 to SLA-10 cells were isolated from 10 fetusesat day 28 of pregnancy. Fetuses were mashed through a 60-mesh metalscreen using curved surgical forceps slowly so as not to generateexcessive heat. The cell suspension was then pelleted and resuspended in30 ml of DMEM containing 10% FCS, 1× nonessential amino acids, 2 ng/mlbFGF, and 10 μg/ml gentamycin. Cells were seeded in 10-cm dishes,cultured one to three days, and cryopreserved. For transfections, 10 μgof linearized vector DNA was introduced into 2 million cells byelectroporation. Forty-eight hours after transfection, the transfectedcells were seeded into 48-well plates at a density of 2,000 cells perwell and were selected with 250 μg/ml of G418.

Knockout Vector Construction

Two alpha-1,3-GT knockout vectors, pPL654 and pPL657, were constructedfrom isogenic DNA of two primary porcine fetal fibroblasts, SLAT-10 andPCFF4-2 cells. A 6.8-kb alpha-1,3-GT genomic fragment, which includesmost of intron 8 and exon 9, was generated by PCR from purified DNA ofSLAT-10 cells and PCFF4-2 cells, respectively. The unique EcoRV site atthe 5′ end of exon 9 was converted into a SalI site and a 1.8-kbIRES-neo-poly A fragment was inserted into the SalI site. IRES (internalribosome entry site) functions as a translation initial site for neoprotein. Thus, both vectors have a 4.9-kb 5′ recombination arm and a1.9-kb 3′ recombination arm (FIG. 6).

3′PCR and Long-Range PCR

Approximately 1,000 cells were resuspended in 5 μl embryo lysis buffer(ELB) (40 mM Tris, pH 8.9, 0.9% Triton X-100, 0.9% NP40, 0.4 mg/mlProteinase K), incubated at 65° C. for 15 min to lyse the cells andheated to 95° C. for 10 min to inactivate the Proteinase K. For 3′ PCRanalysis, fragments were amplified using the Expand High Fidelity PCRsystem (Roche Molecular Biochemicals) in 25 μl reaction volume with thefollowing parameters: 35 cycles of 1 min at 94° C., 1 min at 60° C., and2 min at 72° C. For LR-PCR, fragments were amplified by using TAKARA LAsystem (Panvera/Takara) in 50 μl reaction volume with the followingparameters: 30 cycles of 10 s at 94° C., 30 s at 65° C., 10 min+20 sincrease/cycle at 68° C., followed by one final cycle of 7 min at 68° C.3′PCR and LR-PCR conditions for purified DNA was same as cells exceptthat 1 μl of purified DNA (30 μg/ml) was mixed with 4 μl ELB.

Southern Blot Analysis of Cell Samples

Approximately 106 cells were lysed overnight at 60° C. in lysis buffer(10 mM Tris, pH 7.5, 10 mM EDTA, 10 mM NaCl, 0.5% (w/v) Sarcosyl, 1mg/ml proteinase K) and the DNA precipitated with ethanol. The DNA wasthen digested with BstEII and separated on a 1% agarose gel. Afterelectrophoresis, the DNA was transferred to a nylon membrane and probedwith the 3′-end digoxigenin-labeled probe. Bands were detected using achemiluminescent substrate system (Roche Molecular Biochemicals).

Results

Antibiotic (G418) resistant colonies were screened by 3′ PCR withneo442S and αGTE9A2 as forward and reverse primers. Neo442S is at the 3′end of the neo gene and αGTE9A2 is at the 3′ end of exon 9 in sequenceslocated outside of the 3′ recombination arm (FIG. 6). Therefore, onlythrough successful targeting at the α1,3GT locus would the expected 2.4kb PCR product be obtained. From a total of seven transfections in fourdifferent cell lines, 1105 G418 resistant colonies were picked, of which100 (9%) were positive for α1,3 GT gene disruption in the initial 3′ PCRscreen (range 2.5-12%). Colonies 657A-A8, 657A-I6, and 657A-I11 showedthe expected 2.4 kb band, while control PCFF4-6 cells, and another G418resistant colony, 657A-P6, were negative. A portion of each 3′ PCRpositive colony was frozen down immediately, in several small aliquots,for future use in NT experiments, while the rest of cells were expandedfor long-range PCR (LR-PCR) and Southern analysis.

Since PCR analysis to detect recombination junctions, or mRNA analysis(RT-PCR) can generate false positive results, a long-range PCR, whichwould encompass the entire targeted region, was performed. The LR-PCRcovers the 7.4 kb α1,3GT genomic sequence from exon 8 to the end of exon9, with both primers (αGTE8S and αGTE9A2) located outside of therecombination region (FIG. 2). The control PCFF4-6 cells, and the 3′PCR-negative colony, 657A-P6, showed only the endogenous 7.4 kb bandfrom the wild-type α1,3GT locus. In contrast, three of the 3′ PCRpositive colonies, 657A-A8, 657A-I6 and 657A-I11, showed both the 7.4 kbendogenous band, and a new 9.2 kb band, of the size expected fortargeted insertion of the 1.8 kb IRES-neo cassette into the α1,3GTlocus.

Approximately half (17/30) of the LR-PCR positive colonies weresuccessfully expanded to yield sufficient cell numbers (1×106 cells) forSouthern analysis. It was anticipated that the colonies would beheterozygous for knockout at the α1,3 GT locus, and thus they shouldhave one normal, unmodified gene copy, and one disrupted copy of theα1,3 GT gene. With BstEII digestion, the α1,3 GT knockout cells shouldshow two bands: one 7 kb band of the size expected for the endogenousα1,3 GT allele, and a 9 kb band characteristic of insertion of theIRES-neo sequences at the α1,3 GT locus (FIG. 2). All 17 LR-PCR positivecolonies were confirmed by Southern analysis for the knockout. The samemembranes were re-probed with sequences specific for neo and the 9 kbband was detected with the neo probe, thus confirming targeted insertionof the IRES-neo cassette at the disrupted α1,3GT locus.

Example 2 Production of Porcine Cells Homozygous for the Alpha-1,3-GTGene

Heterozygous alpha-1,3-GT knockout fetal fibroblasts, (657A-I11 1-6)cells, were isolated from a day-32 pregnancy as described above (Seealso Dai et al. Nature Biotechnology 20:451 (2002)). After removing thehead and viscera, some fetuses were washed with Hanks' balanced saltsolution (HBSS; Gibco-BRI, Rockville, Md.), placed in 20 ml of HBSS, anddiced with small surgical scissors. The tissue was pelleted andresuspended in 50-ml tubes with 40 ml of DMEM and 100 U/ml collagenase(Gibco-BRL) per fetus. Tubes were incubated for 40 min in a shakingwater bath at 37° C. The digested tissue was allowed to settle for 3-4min and the cell-rich supernatant was transferred to a new 50-ml tubeand pelleted. The cells were then resuspended in 40 ml of DMEMcontaining 10% fetal calf serum (FCS), 1× nonessential amino acids, 1 mMsodium pyruvate (Gibco-BRL), and 2 ng/ml basic fibroblast growth factor(bFGF; Roche Molecular Biochemicals, Indianapolis, Ind.) and seeded into10-cm dishes. All cells were cryopreserved upon reaching confluence.After removing the head and viscera, some fetuses were washed withHanks' balanced salt solution (HBSS; Gibco-BRI, Rockville, Md.), placedin 20 ml of HBSS, and diced with small surgical scissors. Fetuses weremashed through a 60-mesh metal screen (Sigma, St. Louis, Mo.) usingcurved surgical forceps slowly so as not to general excessive heat. Thecell suspension was then pelleted and resuspended in 30 ml of DMEMcontaining 10% FCS, 1× nonessential amino acids, 2 ng/ml bFGF, and 10μg/ml gentamycin. Cells were seeded in 10-cm dishes, cultured one tothree days, and cryopreserved. For transfections, 10 μg of linearizedvector DNA was introduced into 2 million cells by electroporation.Forty-eight hours after transfection, the transfected cells were seededinto 480-well plates at a density of 2,000 cells per well and wereselected with 250 μg/ml of G418 (Gibco-BRL). An ATG (startcodon)-targeting alpha-1,3-GT knockout vector was constructed (pPL680),which also contained a neo gene, to knock out the second allele of thealpha-1,3-GT gene. These cells were transfected by electroporation withpPL680 and selected for the alpha1,3Gal-negative phenotype with purifiedC. difficile toxin A (described below).

Example 3 Selection with C. difficile Toxin a for Porcine CellsHomozygous for the Alpha-1,3-GT Gene

Toxin A Cyototoxicity Curve

Porcine cells (PCFF4-6) were exposed for 1 hour or overnight to ten-foldserial dilutions of toxin A (0.00001 g/ml to 10 g/ml). Cells werecultured in 24 well plates and were incubated with the toxin for 1 houror overnight at 37 C. The results of this exposure are detailed in Table2. Clearly, a 1 hour exposure to toxin A at >1 g/ml resulted in acytotoxic effect on >90% of the cells. A concentration of toxin A at orslightly above 1 g/ml therefore was chosen for selection of geneticallyaltered cells.

TABLE 2 Toxin A toxicity at 1 hour and overnight exposure [Toxin A],μg/ml 1 hour incubation Overnight incubation 0 100% confluency 100%confluency .00001 100% confluency 100% confluency .0001 100% confluency100% confluency .001 100% confluency 100% confluency .01 100% confluency50% confluency, 50% rounded .1 90% confluency Same as 10 ug/ml 1 >90%rounded Same as 10 ug/ml 10 All cells rounded up All cells rounded up,some lifted

Disaggregated cells from a porcine embryo (I-11:1-6) which contained apreviously identified targeted knockout in one allele of the galalpha-1,3-GT gene (Dai et al.) were transfected with 10 ug linearizedvector DNA (promoter trap) by electroporation. After 48 hours, the cellswere seeded into 48 well plates at a density of 2000 cells per well andselected with 250 ug/ml G418. Five days post-transfection, media waswithdrawn from the wells, and replaced with 2 ug/ml toxin A in culturemedia (DMEM high glucose with 2.8 ng/ml bFGF and 20% FCS). Cells wereexposed to the selective effect of toxin A for 2 hours at 37 C. Thetoxin A-containing media, along with any affected cells that havereleased from the plate surface, was withdrawn, the remaining cellswashed with fresh media, and the media without toxin A replaced. Tendays later, cells were again exposed to toxin A at 1.3 ug/ml in mediafor 2 hours at 37 C. The media, toxin A, and any cells in solution wereremoved, the remaining cells washed, and the media replaced.

Sixteen days post-transfection, a single colony that exhibited toxin Ainsensitivity, designated 680B1, was harvested and a portion sent forDNA analysis and lectin staining DNA analysis indicated that the toxin Ainsensitivity was not due to integration of the second target vector;however, the cells did not stain with GSL IB-4 lectin, indicating that afunctional knockout of the locus had occurred. The 680B1 double knockoutcells were used for nuclear transfer into 5 recipients and threepregnancies resulted. Two of these pregnancies spontaneously aborted inthe first month; the four fetuses from the remaining pregnancy wereharvested on day 39 of the pregnancy and the cells disaggregated andseeded into tissue culture. These fetal cells (680B1-1, 680B1-2,680B1-3, 680B1-4) were exposed to toxin A at 1 ug/ml for 1 hour at 37 C,followed by medium removal, cell washing, and medium replacement withouttoxin A. Fetuses 1,2, and 4 were not affected by toxin A, whereas mostof the cells from fetus 3 rounded up, indicating that this embryo wassensitive to the cytotoxic effects of the toxin A.

Fetuses 1,2, and 4 did not bind GS IB4 lectin, as indicated by FACSanalysis (see Table 3), while fetus 3 did bind lectin. This suggeststhat fetuses 1, 2, and 4 do not carry the epitope alpha 1,3 gal forwhich this particular lectin is specific.

TABLE 3 FACS Results of 680B1-1 to 680B1-4 Cells with GS-IB4 Lectin GSIB4 lectin positive cells (%) 50 μg/ml 100 μg/ml Cell Unstaining IB4lectin IB4 lectin HeLa Cells (Negative  1%  2% 2.8% CTL) PCFF4-6 cells(Positive 0.2% 76%  91% CTL) PFF4 cells (Positive 1.5% 82%  94% CTL)680B 1-1 cells 0.6% 0.8%  0.9% 680B 1-2 cells 1.2% 1.2%  1.1% 680B1-3cells  8% 35%  62% 680B1-4 cells 0.6% 0.8%  0.9%

A complement fixation assay was run on cells from all four fetuses. Thecomplement lysis assay was developed as a bioassay for lack of alpha galexpression. Human serum contains high levels of pre-formed antibodyagainst alpha gal as well as the full portfolio of complement regulatoryproteins (the C3 pathway). The presence of alpha gal on the surface of acell, upon binding of anti-alpha gal antibody, activates the complementcascade, and results in complement-mediated cell lysis. Alpha-galnegative cells would be resistant to complement mediated lysis. In threeseparate tests, B1 and control pig cells were exposed to human serumplus complement, and assays performed to evaluate sensitivity orresistance to alpha-gal-initiated, complement-mediated cell lysis. Theassay was performed with B1-1, B1-2, and B1-4 cells, as well asheterozygous GT KO cells (B1-3, gal positive), and with wild-typealpha-gal (+) PCFF4-6 pig cells as a control. Cells were exposed to oneof three treatments; two negative controls, bovine serum albumin (BSA),and heat-inactivated human serum (HIA-HS) do not contain any functionalcomplement protein and thus would not be expected to cause anysignificant cell lysis; the third treatment, non-heat-inactivated humanserum (NHS) contains functional human complement as well as anti-galspecific antibodies, and thus would be expected to lyse cells which havegalactose alpha 1,3 galactose on their cell surface.

The results shown in FIG. 1 clearly demonstrate that B1-1, B-2 and B1-4cells are resistant to human complement-mediated lysis while B1-3 cells,which is α1,3 Gal positive, is still as sensitive to human plasma as arewild-type PCFF4-6 cells.

Sequencing results of cDNA from all fetuses indicated that fetuses 1,2and 4 contain a point mutation in the second alpha 1,3 GT allele, achange that could yield a dysfunctional enzyme (see FIG. 2). Thismutation occurred at bp424 of the coding region, specifically, thesecond base pair of exon 9, of the alpha-1,3-GT (GGTA1) gene (GenBankAccession No. L36152) as a conversion of a thymine to a guanine residue,which results in an amino acid substitution of tyrosine at aa 142 to anaspartic acid.

This is a significant conversion, as the tyrosine, a hydrophilic aminoacid, is a critical component of the UDP binding site of alpha 1,3GT(see FIG. 3). Analysis of the crystal structure of bovine alpha-1,3-GTprotein showed that this tyrosine is the center of the catalytic domainof the enzyme, and is involved in UDP-Gal binding (Gastinel et. al.,EMBO Journal 20(4): 638-649, 2001). Therefore, a change from tyrosine (ahydrophobic amino acid) to aspartic acid (a hydrophilic amino acid)would be expected to cause disruption of the αGT function (as observed).

To confirm that the mutated cDNA will not make functional αGT protein.,the cDNAs from the second allele of all 4 cells were cloned into anexpression vector and this GT expression vector transfected into humanfibroblast cells (HeLa cells) as well as into primary Rhesus monkeycells. As humans and Old World monkeys lack a functional alpha 1,3 GTgene, the HeLa cells would not have an alpha 1,3 galactose on their cellsurface (as assayed by lectin binding experiments). Results showed thatthe HeLa and monkey cells, when transfected with cDNA obtained fromB1-1, B1-2 and B1-4 cells, were still α1,3 Gal negative by IB4-lectinstaining, while Hela and Rhesus monkey cells transfected with cDNA fromthe B1-3, made a functional alpha 1,3 GT transcript and subsequentlywere α1,3Gal positive. Clearly, cells with the aspartate mutation(instead of tyrosine) cannot make functional alpha 1,3 galactosyltransferase

Example 4 Generation of Cloned Pigs Using Homozygous Alpha 1,3GT-Deficient Fetal Fibroblasts as Nuclear Donors

Preparation of Cells for Nuclear Transfer.

Donor cells were genetically manipulated to produce cells homozygous foralpha 1,3 GT deficiency as described generally above. Nuclear transferwas performed by methods that are well known in the art (see, e.g., Daiet al., Nature Biotechnology 20: 251-255, 2002; and Polejaeva et al.,Nature 407:86-90, 2000).

Oocytres were collected 46-54 h after the hCG injection by reverse flushof the oviducts using pre-warmed Dulbecco's phosphate buffered saline(PBS) containing bovine serum albumin (BSA; 4 gl⁻¹) (as described inPolejaeva, I. A., et al. (Nature 407, 86-90 (2000)). Enucleation of invitro-matured oocytes (BioMed, Madison, Wis.) was begun between 40 and42 hours post-maturation as described in Polejaeva, I. A., et al.(Nature 407, 86-90 (2000)). Recovered oocytes were washed in PBScontaining 4 gl⁻¹ BSA at 38° C., and transferred to calcium-freephosphate-buffered NCSU-23 medium at 38° C. for transport to thelaboratory. For enucleation, we incubated the oocytes in calcium-freephosphate-buffered NCSU-23 medium containing 5 μg ml⁻¹ cytochalasin B(Sigma) and 7.5 μg ml⁻¹ Hoechst 33342 (Sigma) at 38° C. for 20 min. Asmall amount of cytoplasm from directly beneath the first polar body wasthen aspirated using an 18 μM glass pipette (Humagen, Charlottesville,Va.). We exposed the aspirated karyoplast to ultraviolet light toconfirm the presence of a metaphase plate.

For nuclear transfer, a single fibroblast cell was placed under the zonapellucida in contact with each enucleated oocyte. Fusion and activationwere induced by application of an AC pulse of 5 V for 5 s followed bytwo DC pulses of 1.5 kV/cm for 60 μs each using an ECM2001 ElectrocellManipulator (BTX Inc., San Diego, Calif.). Fused embryos were culturedin NCSU-23 medium for 1-4 h at 38.6° C. in a humidified atmosphere of 5%CO₂, and then transferred to the oviduct of an estrus-synchronizedrecipient gilt. Crossbred gilts (large white/Duroc/landrace) (280-400lbs) were synchronized as recipients by oral administration of 18-20 mgRegu-Mate (Altrenogest, Hoechst, Warren, N.J.) mixed into their feed.Regu-Mate was fed for 14 consecutive days. Human chorionic gonadotropin(hCG, 1,000 units; Intervet America, Millsboro, Del.) was administeredintra-muscularly 105 h after the last Regu-Mate treatment. Embryotransfers were done 22-26 h after the hCG injection.

Toxin A was then used to selected the porcine fibroblasts as nucleardonors that were produced as described in detail herein above.

Embryo Transfers and Resulting Live Births.

In the initial attempt to produce live alpha-1,3-GT dKO pigs by nucleartransfer, a total of 16 embryo transfers were performed with geneticallymanipulated donor cells. Nine initial pregnancies were established butonly two went beyond Day 75 of gestation. Five piglets were born on the25th of July 2002. One piglet died immediately after birth and anotherfour were born alive and appeared normal (FIG. 4).

Example 5 Analysis of Homozygous Alpha 1,3 GT Knockout Pigs

Tail fibroblast cells and umbilicus tissue sections were obtained fromall 5 double knockout piglets and stained using the GS-IB4 lectin asdescribed previously. No staining was observed, indicating a completelack of galactose alpha 1,3 galactose epitope on the surface of tissuesfrom these animals (data not shown). Aorta endothelial cells and muscleand tail fibroblasts isolated from the dead piglet (761-1) were negativewith GS-IB4 lectin staining FACS analysis of muscle fibroblasts frompiglet 761-1 also showed a negative result for GS-IB4 binding. Tissuesections of liver, kidney, spleen, skin, intestine, muscle, brain,heart, pancreas, lung, aorta, tongue, umbilicus, and tail obtained frompiglet 761-1 were all negative with GS-IB4 staining, indicating acomplete lack of detectable cell surface alpha 1,3Gal epitopes (Phelpset al., Science 299: 411-414, 2003 including figure S3).

We performed an in vivo immunogenicity test with alpha 1,3GT-knockoutmice. We injected islet-like cell clusters (ICCs) isolated from thepancreas of piglet 761-1 intraperitoneally into alpha 1,3GT knockoutmice. We used ICCs from a neonatal wild-type piglet as a control. Asshown in FIG. 5, no increase in the titer of immunoglobulin M (IgM) toalpha1,3Gal was observed in alpha 1,3GT knockout mice after injectionwith ICCs from the alpha 1,3GT DKO piglet, in contrast to significantIgM titer increases observed in those mice injected with wild-typepiglet ICCs (Phelps et al., Science 299: 411-414, 2003 including figureS4). This result clearly demonstrates that the DKO piglet cells do notmake any alpha 1,3Gal epitopes.

Sequencing of DNA obtained from all five piglets confirmed the presenceof the mutation at by 424 of the GGTA1 gene, as observed in the 680B1-2cells used to clone these animals (FIG. 2).

Since this first successful production of a litter of alpha-GT dKO pigs,two subsequent litters of dKO piglets have been produced by nucleartransfer, in one case (litter 662) using the dKO fetal fibroblasts asnuclear donor cells. Litter 660 was produced by nuclear transfer usingtail fibroblast cells from a member of the litter 761 as nuclear donor.These births are summarized in Table 4.

TABLE 4 Summary of alpha-GT double knockout births produced by nucleartransfer Cell Line No. Litters No. Live piglets produced A 8 14 B 2 2 C1 1 Total 17* PM=GT allele knockout via point mutation; Neo=GT allele knockout viahomologous recombination and insertion of Neo selectable marker gene.All pigs presented in this table are homozygous GT knockouts.

Example 6 Breeding of Heterozygous Alpha 1,3 GT Single Knockout (SKO)Male and Female Pigs to Establish a Miniherd of Double Knockout (DKO)Pigs

Southern blot confirmed cloned GT-SKO females and male cloned pigs havebeen generated. Male and female heterozygous (single gene alpha1,3GTknockout pigs) have been bred by natural breeding and by artificialinsemination (AI), in order to generate a herd of DKO pigs for use inpreclinical studies and human clinical trials.

Example 7: Decellularization of Dermal Tissue from Double KnockoutAnimals

The biological tissue to be processed is first procured or harvestedfrom an animal donor in which functional alpha 1,3GT has beeninactivated, for example in pigs, as described above. Dermal tissue isexcised from the donor animal using a dermatome or other device known toone skilled in the art. The tissue is placed in a stabilizingtransportation solution which arrests and prevents osmotic, hypoxic,autolytic and proteolytic degradation, protects against bacterialcontamination and reduces mechanical damage that can occur. Thestabilizing solution generally contains an appropriate buffer, one ormore antioxidants, one or more oncotic agents, an antibiotic, one ormore protease inhibitors, as described herein or known to one of skillin the art.

The tissue is then incubated in a processing solution to remove viableantigenic cells (including epithelial cells, endothelial cells, smoothmuscle cells and fibroblasts) from the structural matrix withoutdamaging the basement membrane complex or the structural integrity ofthe collagen matrix. The processing solution generally contains anappropriate buffer, salt, an antibiotic, one or more detergents, one ormore protease inhibitors, and/or one or more enzymes as described hereinor known to one skilled in the art. Treatment of the tissue with thisprocessing solution is done at a concentration for a period of time suchthat degradation of the basement membrane complex is avoided and thestructural integrity of the matrix is maintained including collagenfibers and elastin to produce decellularized tissue.

After the tissue is decellularized, it is incubated in acryopreservation solution. This solution generally contains one or morecryoprotectants to minimize ice crystal damage to the structural matrixthat could occur during freezing, and one or more dry-protectivecomponents, to minimize structural damage alteration during drying andmay include a combination of an organic solvent and water whichundergoes neither expansion or contraction during freezing. Followingincubation in this cryopreservation solution, the tissue is packagedinside a sterile container. As an additional or alternate method, thedecellularized tissue matrix is fixed with a crosslinking agent such asglutaraldehyde and stored prior to transplantation.

Example 8: Ligament Harvesting for Xenografts from Double KnockoutAnimals

The biological tissue to be processed is first procured or harvestedfrom an animal donor in which functional alpha 1,3GT has beeninactivated, as described herein. Ligament tissue is excised from thedonor animal using an appropriate surgical technique. In the first step,an intact ligament is removed from the knee of a non-human animal. Thejoint which serves as the source of the ligament is collected fromfreshly killed animals and immediately placed in a suitable sterileisotonic or other tissue preserving solution. Harvesting of the jointsoccurs as soon as possible after slaughter of the animal and performedin the cold, i.e., in the approximate range of about 5° C. to about 20°C., to minimize enzymatic degradation of the ligament tissue. Theligament is harvested alone or the ligament is harvested with a block ofbone attached to one or both ends. A block of bone representing acylindrical plug of approximately 9-10 mm in diameter by 20-40 mm inlength is left attached to the ligament. The ligament is carefullyidentified and dissected free of adhering tissue. The xenograft is thenwashed in about ten volumes of sterile cold water to remove residualblood proteins and water soluble materials. The xenograft is thenimmersed in alcohol at room temperature for about five minutes, tosterilize the tissue and to remove non-collagenous materials.

After alcohol immersion, the xenograft is implanted into a knee.Alternatively, the xenograft is subjected to at least one of thefollowing treatments: radiation treatment, treatment with alcohol orozonation, one or more cycles of freezing and thawing, and/or treatmentwith a chemical cross-linking agent. In the freeze/thaw cyclingtreatment, the xenograft is thawed by immersion in an isotonic salinebath at room temperature (about 25° C.) for about ten minutes. Noexternal heat or radiation source is used, in order to minimize fiberdegradation.

In addition or alternatively, the xenograft is subjected to a cellulardisruption treatment to kill the cells of the ligament prior to in vitrodigestion of the xenograft with glycosidases. After surface carbohydratemoieties are removed from nucleated cells and extracellular components,nucleated cells, i.e., living cells reexpress the surface carbohydratemoieties.

In addition or alternatively, either before or after the ligament cellsare killed, the xenograft is subject to in vitro digestion of thexenograft with glycosidases, enzymatically eliminate antigenic surfacecarbohydrate moieties. Other enzymes may also be used, in order toremove any residual non-alpha gal carbohydrate moieties.

Prior to implantation, the ligament xenograft of the invention istreated with limited digestion by proteolytic enzymes such as ficin ortrypsin to increase tissue flexibility or coated with anticalcificationagents, antithrombotic coatings, antibiotics, growth factors, or otherdrugs known in the art to enhance the incorporation of the xenograftinto the recipient knee joint. Additionally or alternatively, theligament xenograft is further sterilized using known methods, forexample, with additional glutaraldehyde or formaldehyde treatment,ethylene oxide sterilization, propylene oxide sterilization, or thelike. The xenograft is stored frozen until required for use.

The ligament xenograft, or a segment thereof, is implanted into adamaged human knee joint by those of skill in the art using knownarthroscopic surgical techniques. Specific instruments for performingarthroscopic techniques are known to those of skill in the art, whichensure accurate and reproducible placement of ligament implants.Initially, complete diagnostic arthroscopy of the knee joint isaccomplished using known methods. The irreparably damaged ligament isremoved with a surgical shaver. The anatomic insertion sites for theligament are identified and drilled to accommodate a bone plug. The sizeof the bone plug is about 9-10 mm in width by about 9-10 mm in depth by20-40 mm in length. The xenogeneic ligament is brought through the drillholes and affixed with interference screws. Routine closure isperformed.

Example 9: Tissue Grafts Derived from Small Intestine Submucosa (SIS)from Homozygous Alpha 1,3 Gal Knockout Pigs

The tissue graft material is derived from an animal, such as a pig,lacking any functional expression of alpha 1,3 GT, and containssubmucosa tissue and basilar mucosa tissue delaminated from a segment ofthe small intestine, such as the jejunum, a division of the smallintestine extending between the duodenum and the ileum.

A SIS graft obtained from the small intestine of alpha 1,3 gal deficientpigs is prepared by first resecting a segment of autogenous proximaljejunum following a midline laparotomy incision. The resected segment ofjejunum is then wrapped in surgical sponges which have been soaked inphysiologic saline. Upon completion of the intestinal anastomosis, theexcised intestinal segment is prepared by abrading intestinal tissue toremove the outer layers including both the tunica serosa and the tunicamuscularis and the inner layers including at least the luminal portionof the tunica mucosa. Under conditions of mild abrasion the tunicamucosa is delaminated between the stratum compactum and the laminapropria. More particularly, following removal of any mesenteric tissuesfrom the intestinal segment utilizing, for example, using Adson-Brownforceps and Metzenbaum scissors, the tunica serosa and the tunicamuscularis (the outer tissue layers) are delaminated from the intestinalsegment by abrasion using a longitudinal wiping motion with a scalpelhandle and moistened gauze. Following eversion of the intestinalsegment, the luminal portion of the tunica mucosa is delaminated fromthe underlying tissue using the same wiping motion. Care is taken toprevent perforation of the submucosa. Also, any tissue “tags” from thedelaminated layers remaining on the graft surface are removed.Optionally, the intestinal segment may be everted first, then strippedof the luminal layers, then reinserted to its original orientation forremoval of the tunica serosa and the tunica muscularis. The graftmaterial is a whitish, translucent tube of tissue approximately 0.1 mmthick, typically consisting of the tunica submucosa with the attachedlamina muscularis mucosa and stratum compactum. For vascular graftpreparation, the prepared graft is everted to its original orientationso that the stratum compactum serves as the luminal surface of thegraft.

The prepared graft material is typically rinsed with saline and placedin a 10% neomycin sulfate solution for approximately 20 minutes, afterwhich time the graft material is ready for use. The grafts are appliedusing routine surgical procedures commonly employed for tissue graftapplications. For use in non-vascular tissue graft applications, thetubular graft material is cut longitudinally and rolled out to form a“patch” of tissue. The entire tissue delamination procedure describedabove can be carried out on “patches” of intestinal tissue prepared bycutting the intestinal segment longitudinally and “unrolling” it to forma pre-graft patch. The prepared graft tissue patches can be utilized,for example, as a skin graft material, for dura repair, or for repair ofother body tissue defects lending themselves to surgical application ofa tissue graft patch having the physical and functional characteristicsof the present graft composition. Other applications for Gal KO SISpatch material include for rotator cuff repair, hernia, abdominal wallrepair, slings to treat urinary incontinence, burns, skin replacement,cosmetic surgery including breast reconstruction, facial defects, lipreconstruction, eyelid spacer grafts, depressed scar repair, mucosalgrafts, nasolavial folds, oral resurfacing, parotidectomy, septalperforation repair, rhinoplasty, temporary wound dressing, woundcoverage, tympanoplasty, vestibuloplasty, and other soft tissue defects.

For use in vascular grafts, the diameter of the graft is approximatelythe same as the diameter of the recipient blood vessel. This isaccomplished by manipulating the tissue graft to define a cylinderhaving a diameter approximately the same as that of the recipient bloodvessel and suturing or otherwise securing the tissue graftlongitudinally to form said vascular graft. Thus, for example, avascular graft is prepared by selecting a sterile glass rod having anouter diameter equal to that of the recipient blood vessel andintroducing the glass rod into the graft lumen. Redundant tissue is thengathered and the desired lumen diameter achieved by suturing along thelength of the graft (for example, using two continuous suture lines or asimple interrupted suture line) or by using other art-recognized tissuesecuring techniques (see also U.S. Pat. No. 4,956,178).

The invention described herein can be practiced in the absence of anyelement or elements, limitation or limitations which is not specificallydisclosed herein. The terms and expressions that have been employed areused as terms of description and not of limitation, and there is nointention that in the use of such terms and expressions of excluding anyequivalents of the features shown and described or portions thereof, butit is recognized that various modifications are possible within thescope of the invention claimed. Thus, it should be understood thatalthough the present invention has been specifically disclosed herein,optional features, modification and variation of the concepts hereindisclosed can be resorted to by those skilled in the art, and that suchmodifications and variations are considered to be within the scope ofthis invention as defined by the appended claims. In addition, wherefeatures or aspects of the invention are described in terms of Markushgroups, those skilled in the art will recognize that the invention isalso thereby described in terms of any individual member or subgroup ofmembers of the Markush group.

We claim:
 1. A tissue product comprising a tissue stripped of viablecells wherein the tissue is derived from a tissue of a porcine animal inwhich both alleles of the alpha-1,3-galactosyltransferase gene areinactive, wherein at least one allele is rendered inactive through atleast one point mutation, and the animal lacks expression ofalpha-1,3-galactosyltransferase.
 2. The tissue product of claim 1,wherein the tissue is a hard tissue.
 3. The tissue product of claim 1,wherein the tissue is a soft tissue.
 4. The tissue product of claim 2,wherein the hard tissue is bone or a fragment or derivative thereof. 5.The tissue product of claim 3, wherein the soft tissue is selected fromthe group consisting of skin, dermal, submucosal, ligament, tendon andcartilage or a fragment or derivative thereof.
 6. The tissue product ofclaim 1, wherein the tissue is a combination of hard and soft tissue. 7.The tissue product of claim 6, wherein the tissue is a bone-tendon-bonegraft.
 8. The tissue product of claim 1, wherein at least one allele ofthe alpha-1,3-GT gene is rendered inactive by a genetic targeting event.9. The tissue product of claim 8, wherein the genetic targeting event ishomologous recombination.
 10. The tissue product of claim 8 or 9,wherein the genetic targeting event uses a targeting construct directedto exon 9 of the alpha-1,3-GT gene.
 11. The tissue product of claim 8,wherein both alleles of the alpha-1,3-GT gene are rendered inactivethrough at least one point mutation.
 12. The tissue product of claim 8,wherein the at least one point mutation of the alpha-1,3-GT gene is asubstitution, deletion or insertion mutation or a combination thereof.13. The tissue product of claim 8, wherein at least one point mutationof the alpha-1,3-GT gene is a T-to-G point mutation at the second baseof exon
 9. 14. The tissue product of claim 13, wherein the T-to-G pointmutation at the second base of exon 9 in both alleles of thealpha-1,3-GT gene.
 15. The tissue product of claim 8, wherein an alleleof the alpha-1,3-GT gene is rendered inactive through at least two pointmutations.
 16. The tissue product of claim 8, wherein the tissuestripped of viable cells is produced by enzymatic treatment.
 17. Thetissue product of claim 8, wherein the tissue is bone.
 18. The tissueproduct of claim 8, wherein the tissue stripped of viable cells isproduced by chemical treatment.
 19. The tissue product of claim 8,wherein the tissue is selected from the group consisting of tendon,joint, bone and heart valve.
 20. The tissue product of claim 9 or 11,wherein the tissue can be further processed via crosslinking treatments.21. The tissue product of claim 17 or 19, wherein the tissue can befurther processed via additional chemical treatments.